Proceedings of the American Academy of Arts and Sciences, Vol. 35, No. 15 (Feb., 1900), pp. 283-304 The metamerism of the Hirudinea [1/1, 1 ed.]

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CONTRIBUTIONS FROM THE ZOOLOGICAL LABORATORY OF THE MUSEUM OF COMPARATIVE ZOOLOGY AT HARVARD COLLEGE. L.

E.

?

DIRECTOR.

MARK,

THE

No.

108.

OF

METAMERISM By

E.

W.

THE

HIRUDINEA.

Castle.

Received January 20, Presented by E. L. Mark, February 14, 1900.

CONTENTS. I.

.

Introduction.

II.

Limits

the

of

.... Rhynchobdellidae as a Criterion 1. Neuromeres Somite a. 2.

286 of

2.

in Glos

Reduction

IV.

siphonia.287 and other Metameric as Criteria of So Organs the

V.

in the

I.

are

not

all

alike,

but

are

293 296 ....

Primitive

Condition

of

Gratiolet on

the

internal

1862 Gratiolet L.,

fall they succession

organs

but

called

exterior

with

rings the groups

of

of

two

the

body

of

the 300

Somite.

into

the

pointed successive

similar

groups

out rings of five

in the greater throughout repeated regular a nerve in each such group found He single ganglion body. in other he discovered that of nephropores; words, pair segmentation external single

297 299

Introduction.

medicinalis that

291

302 Summary. 303 Papers cited.

long ago as the year leech, Hirudo

. in Nephe

Reduction

lis. Somite Growth. 1. Rhynchobdellidae

Leech

Somite

to of So

Type

2. Gnathobdellidae.

Gnathobdellidae.291

medicinal

Somite

Limits.290 of

of Five-ringed

Three-ringed mite

Septa

Limits

As

1. Relation

Limits.286

Somite

mite III.

285

in the

Somite

(metamerism) of the groups " zoonites rings natural

which

that

in the

of

body which

each,

of

part a

and there

He

the

single a was

not

agreed

rings. " (somites). which landmarks,

the

with

noticed

indicated

to

dorsally

the ring

which

contains

a pair of pores (nephropores) the

counting Gratiolet indicated

sensory seems

the

expressed

view

in

the

as

should,

such

but

septa,

(sensory

these

and

In

Vaillant

subsequent

; secondly,

ring)

this

convenient

to ring 5,

of

all nearly Vaillant

assumption

unquestioningly. be more logical mark the limits

believed

landmarks

limits

posterior

him

it would

Chaetopoda,

case of Pontobdella,

that

anterior

somites.

that

ganglion

ring assumed

followed

the

the

1.

ring to have

have

investigators

ACADEMY.

lying in the furrow just posterior

as

respectively or units

phological

AMERICAN

These were, first, some whitish flecks (sensillae) found

him their limits. on

THE

OF

PROCEEDINGS

286

to

for

look the

of

do

which

septa,

In

somites.

that he had succeeded

investigators

not

agree

with

the

ends

of

mor

the

subsequent, alone ('70) the

in finding him

in

this

view. Gratiolet

further

observed

that

a

somite

becomes

together.

He

of

number crowded either

in

rings closer

end

distinct

of

the

(Helix,

and

smaller,

that the suggested had resulted from

probably body as is the case

ganglia,

toward

with

the

the

body

are

ganglia

terminal

at ganglion of originally certain Mollusca

a fusion of

ganglia

the

the

etc.). thus

Gratiolet

somites

present

natural

limits

the way

opened directions:

two

in

leech

in the of

these

of body somites.

a study determine

for to

first,

the

first

the metamerism

the

and

leech;

The

of

number

the

primitive to determine the

secondly,

indicated

problem

of

of

has

received

a satisfactory solution through the splendid work of Whitman ('92) on the Rhynchobdellidse, and of Bristol ('99) on the Gnathobdellidae. From

studies

of my

own,

can

confirm

the

I

lication,

the

results

conclusion

of the contains leech body thirty-four The the second problem, namely, the somite, indicated, has, as already To it,

a discussion I

now

of

invite

II.

Limits

of

the

1. Neuromeres

In determining it has

been

these

distinct

are

in process

of

the

received

practically considerations

some

the

as a Criterion

of that

investigators, somites.

determination

in

Somite

to necessary seem natural,

found

of

which

pub the

true

limits

no

attention.

growing

out

of

of

Rhynchobdellid^. of Somite

Limits.

the number of somites found in the body of the leech,

It would

system. for a solution

and

this problem attention.

of of

the

problem

rely

solely

therefore,

concerning

on to

the

a look

limits

of the nervous study in the same direction of

the

somite.

?

CASTLE.

distinct

tributed

HIRUDINEA.

287

('92) has shown that in the genus Glossiphonia

Whitman each

THE

OF

METAMERISM

off

gives to the

ganglion

respectively

of

three

pairs in which

ring

the

(Clepsine) are

which

nerves,

dis lies

typically

ganglion

it (Fig. 1, VIII.).* (sensory ring), the ring before it, and the ring behind we

If

as

neuromeres

take

innervated

to

somite.

According these rings with a innervated from different vir. two

other only of a sensory

posed aware

that

with

any

such

view

facts

which

may

be

discussion graphically

ever

could

be to

limited at

suggested, in its

presented the two

the

is

Figure

1,

body, See

the

left

as com

somite

it, but I am not precede and I am unacquainted support.

before

views

and

right

which

the

regard

which

rings

been

last

a somite.

to

be

a

constituting the however,

Accordingly which

stated,

are of

respectively

margins

1.

Figure

a.

with

tion

the

at

somite

tome the possibility

the

organs on every

occur,

second

those

as

not

extreme

ring,

cases,

each originally two of the three

only its full

the

on

or even regions one. quota

somite

we

of

that neuromere See

indicated

three

on

body

rings,

such we

third

every

fact two

but

reduc

suppose

but

ring, shows

rings,

as

somites must

limits may

somite

1, I.-IV.; Figure sense the metameric

This

rings. contains

regard

of

the method

of

regions of the successive

the If

study

Glossiphonia.

the middle

in

particular

of

body In

2, XXV.-XVII.

Figure

a

was

limits,

of

ends

in Glossiphonia.

Reduction

Somite

first suggested

What coincide

in

would two

has

presented

regarded

represent

ganglion,

thus

rings

as

view, accepted commonly of the next following ring

possible and the

ring a view

three

the

somites, be

should

the

of

The

of

criteria

souree

a common

from

that in

or,

having that one

had or

have This primitive subsequently rings disappeared. as due either to a be explained disappearance might complete suppression an A comparative with of of a ring or to its fusion ring. study adjacent in different of the abbreviated that shows somites Glossiphonia species the

latter

process An

somite.

is

examination

the first step in the abbreviation invariably 1 and 2 will of this clear. make Figures

the case of somite IV. sensory

ring

leaves

of the three three

rings

the

(Fig. 1) a fusion has taken place between ring

in somites III.

occurred * This

and

out of account

nerves innervated

and

which

(Fig. 1) and XXV. a branch

is distributed by

precedes

the ganglion.

it.

A

similar

(Fig. 2).

union

of

a In

the has

In the case of

(d, Fig. 1) which arises from the posterior to sense organs on the dorsal surface of all

PROCEEDINGS OP THE AMERICAN ACADEMY.

288

r.

1. Dorsal view of the anterior part of the body of Glossiphonia para Fig. in the right half of the figure the sitica Say {Clepsine hollensis Whitman), showing nervous in the left half, the lymph The system system; pear-shaped (stippled). sense organs, shown on certain dark bodies d., stump of a nerve rings are dorsal branch

which

on all three rings of a somite. sense dorsal organs Somite limits are indicated va.t, transverse lymph vessel. to Whitman's at the left of the figure according (I.-VII/), to the view of the writer. After Whit according (I.-VIII.),

innervates

npfrpo., nephropore. by roman numerals, at the right view; man ('92), simplified.

CASTLE. ?

I.

somites and

ring one which II.,

and

a fusion

XXVII. the

both

METAMERISM

precedes and XXVI.,

XXV.,

taken

place which

one

rings, intermediate

where

THE

has the

adjacent it. An

OP

the

HIRUDINEA.

between

is found the

following

xx,v/ x'VlII^?--

the as well

follows

condition

ring

289

in

sensory

sensory as the somites is

ring

I^^vJ^xx,v

XXVI/:'s-^/

end of the body of Glossiphonia biocu Fig. 2. Posterior stagnalis L. (Clepsine lata Sav.), dorsal view. Somite limits as commonly are shown at the left placed as the writer of the figure would (XXIII.'-XX VTI.'); them, at the right place (XXIV.-XXVIL). considerably to anterior seen

is thus toward are ?:

either

1. A precedes 2. The 3.

reduced it.

It

fusion

The

to be end

in size, but still distinct amount of shortening which

greater increasingly of the body. The

takes

place

between

the

from the

as one

progresses successive steps

the

sensory

somite

and

sensory

ring

ring

is reduced

from of

ring

undergoes the middle abbreviation

the

ring

which

it. follows ring which fuses with the sensory

the

sensory

in size.

it. preceding we find united at the conclusion this process, in a Accordingly, single ? a sensory three distinct and the two rings ring rings, primitively ring are to it. But the these three rings innervated adjacent from typically same fact This substantiates the view 1, VII., VIII.). (Fig. ganglion limits with somite that neuromere coincide limits. expressed, already that neuromere with limits coincide If we do not admit somite limits, vol.

xxxv.

?19

ring of

OF

PROCEEDINGS

290

Whitman's

(the

value

mites). somite

a

ing rior

untenable.

and

ring

limits

the

innervating realized in all

be

two

marked

rings

end

(Fig. 3, left half, compare Fig.

at the anterior of a absurdity ring the thirty-four and somite somites, the body will contain two rings. only neuromere

of

are of

.

ii.

i^?^)

11/j

2.

.

Septa

.i^ZZ^

(