IN BAPSNIA, AND OF THE STEUCTUEE OF THE EPHIPPIUM. 
93 
which is, I beheve, of great importance, inasmuch as it seems to be characteristic of the 
Podophthalmian, as contradistinguished from the Edriophthalmian embryo, — to have the 
posterior sternal region of the body, or some part of it, at first folded against the anterior. 
“ The hmbs, &c. are now developed in the manner described by Eathke ; but underneath 
the dehcate membranous investment of the embryo, which continues to sheath the anten- 
nules and the antennse as they enlarge, but passes smoothly over the rest of the limbs, 
and eventually extends considerably beyond the end of the abdomen and of the anten- 
nules and antennae, like a glove too long for the fingers. 
“ This ‘ larval skin ’ persists until the embryo has acquired a^th of an inch in length, 
and has assumed very nearly its adult form. It then disappears, probably becoming cast 
in the ordinary manner.” 
So far as I can judge from the figures and descriptions of M. Joly, a very similar 
larval skin is developed, and cast by the embryo of Caridina Desmarestii^ . 
Mr. Spexce Bate also, in p. 55 of his very interesting “ Eeport on the British Edrio- 
phthalma” to the British Association, 1855, observes, — “It is probable, that about the 
middle of the period of incubation, the young animal quits the egg, for we have con- 
stantly taken them from the pouch, bearing an embryonic character without being closed 
in their egg-case. The laiwa at this period is very immature and covered in a general 
tunic, which, apparently without having any absolute vital connexion with the animal 
more than the original egg-case had with the embryo, adapts itself in form to the whole 
creature, and fulfils the duty of a protective tissue.” 
This remarkable fact has been already observed by the accurate STEAUSsf , who compares 
it with the gestation of the marsupials. He says, however, “ Dans cet etat, ils n’offi’ent 
qu’une masse arrondie et informe, sur laquelle on remarque, quand on rexamine de pres, 
les rudiments obtus du bras but here he is in error: the rudimental antennae are not on 
the spherical membrane enclosing the embryo, but are inside it, and are seen through it. 
Very similar also is the hatching of many Annelids, in which also the young animal quits 
the egg, as an egg-shaped body Avithout any external organs except cilia, by means of 
which it SAvims Avith actmty. 
This, hoAveA’er, does not shoAV any disparity in the tAvo cases, for the development of 
the cilia is probably connected Avith the free condition of the young animal, and Avith 
the tendency to the production of these important organs in the Annelids, and their 
constant absence in the Crustacea. 
It would appear, therefore, that the Da^^hnia, so far from undergoing no metamor- 
phosis, does, in fact, enter the Avorld in a very rudimental condition, and that only after 
the first change of skin does it assume the Avell-known characters of the genus. In fact, 
* See M. Jolt’s paper on that Crustacean in the ‘Aunales des Sciences NatureUes,’ t. xii. See also 
‘Annals and Magazine of Natural History’ (February 1857, p. 163) for an account of a similar phenomenon 
in lulus. 
t Loc. cit. p. 417. 
MDCCCLVII. 0 
