M. Ilathke on the Development of the Decapodfs. 365 



present not inconsiderable differences in the more advanced embryo and the old 

 individual. Thus, for example, in the Eriphia spinifrons, when it is about to 

 leave the egg, the antennae are in proportion longer, but the claws shorter 

 and much more slender, than when the animal is grown. Also the tail and 

 the eyes, considered as a whole, are formed long before these Crustacea leave 

 the egg, and are similar to the same organs in the fully grown animal differing 

 only in their proportions. The eyes are in proportion much larger, especially 

 in the Kriphia, in which, during the lust half of its uterine life, they attain an 

 enormous size ; but, of the two principal parts which can ba distinguished in 

 them, it is the outer half or the real eye that is particularly remarkable for 

 its size ; as to the tail, it consists, in the more advanced embryo, of just as 

 many segments as in the grown animal, and is provided with a fan, not only 

 in the species mentioned as having long tails, but even in the Eriphia. I 

 cannot distinctly state the number of parts composing the fans of the Eriphia; 

 but in the embryo of the Palaemon squilla the fan consists of five leaf-like 

 portions. AVith-regard to the relations of the dimensions, it appears, as Ca- 

 volini formerly remarked of another crab, that the tail of the more advanced 

 embryo, of the Eriphia spinifrons, is much longer than in the grown animal, 

 but still very small, and nearly equally broad, and similarly formed, as in the 

 long-tailed Decapodes. In the mere advanced embryo of the Palaemon and 

 Crangon, on the contrary, the tail is comparatively not so thick and fleshy as 

 in the full grown crab of the same species, but siill in other respects it is si- 

 milar. The shield also which, in the full grown individuals, covers the head 

 and the thorax, already exists in the more advanced embryo, and forms on 

 each side a projection which probably covers the gills. I have not, so far as 

 I remember, distinctly seen gills in any embryo of the animals in question 

 probably because these organs are extremely minute. 



Of the internal parts, I have found a heart quite similar to that of the full 

 grown animal in the more advanced embryo of all the above-mentioned crus- 

 tacea ; but a liver, a ganglionic chain, and an intestinal canal, I have seen 

 distinctly, only in the embryo of the Palaemori squilla, for it is only this embryo 

 that can be extracted uninjured from the egg ; but still, on account of their 

 small size, I have not been able to examine the parts satisfactorily. 



From this description, which, however, is merely to be considered as a rough 

 sketch, you may be able to judge for yourself if the Decapodes inhabiting the 

 sea, actually leave the egg in so extremely imperfect a- condition as has been 

 represented by Thompson ? I do not wish to speak of the internal organs, 

 for of their development I know too little ; but as to what concerns the ex- 

 ternal organs, I must confess that, in my opinion, an Eriphia or a Palaemon 

 leaves the egg in a condition not much less im; erfect that is, in relation to 

 its parents than a bird. For such a crustaceous animal has, with the excep^ 

 tion of the male parts of generation, just as many external organs; and these 

 organs, considered separately, are composed of just as many essential portions, 

 and occur as a whole, and, in their separate parts, in the same relative posi- 

 tions as in the old individual. The form also of each part is of such a descrip- 

 tion, that in it we can recognise distinctly enough a certain portion of the 

 perfect animal. Probably, however, there is no animal formed in an egg, 

 whose individual externally observable organs, when it leaves the egg, present 

 collectively and separately the same proportions, as they possess in their ma - 

 lured condition. 



