554 
elapsed before the body of the young my- 
riapod was so far liberated as to remain only 
partially enclosed between the two halves of the 
shell, as represented in fig. 318, being still at- 
tached to its interior by a pe- : 
dicle or funis (fig. 319, d). Fig. 318. 
So remarkable is its condi- 
tion at this period that it 
strongly resembles the ex- 
pansion of the germ in the 
seed of a plant, rather than 
the evolution of a living 
animal. The embryo is per- 
fectly motionless, and the 
bursting of its shell appears 
to be effected not by any 
direct effort of its own, since, up to this time, it 
has acquired only the form and external sem- 
Dlance ofa living animal ; but, by the force of ex- 
pansion of the growing body, the development 
of which being greatest along the dorsal or larger 
curvature, exerts, in consequence, a greater de- 
gree of force against the middle of the dorsal 
than the corresponding part of the ventral sur- 
face; the head and tail of the embryo acting 
as a fulcrum against the ventral surface only at 
the ends of the shell, and thus bending it into 
the kidney-shaped form it assumes, while the 
dorsal surface of the embryo is gradually 
pressed through the opening. From the com- 
parative rapidity of its enlargement imme- 
diately afier the shell is fissured, Mr. Newport 
observes, that it seems as if the stimulus given 
to it by exposure to a new medium, atmo- 
spheric air, were the great means of exciting its 
evolution. 
The embryo is now formed of eight distinct 
segments (fig. 319), including the head, the 
ninth or anal segment being still indistinct. 
The head is more 
defined in its out- 
line, and firmer in 
texture than other 
parts of the body, 
and is __ inflected 
against the under } 
surface of the pro- 
thorax (2) or second 
egment, from which 
it is divided on the 
upper part bya deep 
transverse line: at 
its sides it exhibits 
a faint trace of the future antenne. The four tho- 
racic segments also exhibit on their ventral sur- 
face little nipple-shaped extensions, three of 
which on each side are the rudiments of future 
legs. When viewed from above, the body of the 
embryo appears compressed and wedge-shaped, 
its greatest diameter being in the second and 
third segments, while each succeeding segment 
is more and more contracted. Mr. Newport 
was unable at this period to detect any separate 
internal organs, the whole embryo being still a 
congeries of vesicles or cells, in the midst of 
which there seemed to be some faint traces of 
the commencement of an alimentary canal. 
« At the end of the first day,” continues Mr. 
Newport, “ I carefully removed the embryo and 
shell into diluted spirits of wine, and, on ex- 
Fig. 319. 
MYRIAPODA. 
amination beneath the microscope, found the — 
body of the embryo covered with an exceed. 
ingly delicate cuticle, through which the cells 
it was formed of were distinctly visible. It 
was also completely enclosed in a smooth an 
perfectly transparent membrane (fig. 319, ©) 
which seemed to contain a clear fluid, inte 
between it and the embryo. This men 
rane I regard as the analogue of the amni 
the vitelline or investing membrane of ft 
embryo in the higher animals, and ide 
with the membrana vitelli, before described, 
the proper membrane of the yelk in the e 
Julus. It is a shut sac that completely inves 
the embryo, except at its funnel-shaped %& 
mination at the extremity of the body (fig. 31 
d), where it is constricted, and together wii 
another membrane (e), which in yu 
egg is external to this and lines the interior 
the shell, assists to form the cord or pro 
funis (d). aa 
“The funis enters the body of the embryo 
the posterior part of the dorsal surface of 1 
future penultimate segment, where the mit 
or spine exists in the adult animal, and not 
the dorsal surface of the thoracic region, as § 
by Rathke in the Crustacea. The proper a 
or terminal segment is, as yet, but 
perfectly developed. In the funis @) 
also observed some exceedingly delicate st 
tures that exhibited all the appearane 
vessels. They seemed to enter the body 
two sets, that were spread over and enti 
lost in the membrane (e). Whether these 
indeed vessels, or merely folds of the m 
brane I am not certain. The membrane (¢ 
which they appeared adheres closely to 
shell and retains the embryo in connet 
with it by means of the funis. In the unl 
egg, this is also a shut sac like the am 
and forms the membrana externa or chorion 
the second or outer investing membrane 
ovum lining the interior of the shell. 
: “ The bran: of re two investing 
ranes of the embryo in iapoda may,” 
Mr. Newport, “ be regarded with some int 
in reference to the analogies which they 
to similar structures in Vertebrata, sim 
shew the persistence of one universal lawi 
mode of vise ment of the germ.” 
On the third day the embryo had ¢ 
ably increased in size, but was still per 
motionless and attached:to the shell b 
funis. This attachment continues for | 
days, during which the embryo remains 
tially protected by the two halves of the : 
When examined at this period in thet 
State, all the parts of its body are still” 
tinct, but in specimens that have been 
time in ‘spirits of wine, the divisions! 
the segments are well marked. The ru 
of the legs are more developed, but t 
he uni 
ae 
the second and third segments less tha 
fifth, so that not only at the bursting © 
shell, as noticed by Savi, but also for s¢ 
days afterwards the embryo is competely 
dal, the future limbs existing only in@ 1 
mentary state. Posteriorly to the fifth segm 
the body is more soft and delicate, and the s 
ments less clearly defined. This results fit 
A 
