268 H. Rathke on the Metamorphosis of the Crustacea. 



nearly as thick as broad. At its extremity there was a large 

 irregular triangular plate, which had at its posterior broad 

 margin, or base, a moderately deep but long incisure, and at 

 whose two posteriorly directed corners two long, thick spines 

 directed backwards were inserted (articulated). False legs 

 were already present, not yet divided into two branches, 

 but nearly cylindrical. Two simple appendages, like the false 

 feet, but of smaller size, were inserted on both sides of the 

 lamina, representing the fan, at (into) the hinder extremity of 

 the sixth joint of the tail. 



Together with the above-described larvae were likewise 

 captured some others which had swum deeper. Now these 

 were very much further developed, and already possessed a 

 considerable resemblance to full-grown specimens of Hyas 

 Araneus : for instance, the antennae, foot-jaws and legs were of 

 similar form and relative dimensions as in these ; this was like- 

 wise the case with respect to the dorsal shield, only that this 

 shield terminated in front in three rather long, thick spines, 

 lying nearly in one and the same horizontal plane, of which 

 the central one was larger than the two others. The tail, on 

 the contrary, was proportionately much longer than in full- 

 grown specimens, and was likewise of a moderate breadth and 

 pretty thick. The false feet were very long in comparison to 

 the tail, and were already provided with two branches unequal 

 in size, and furnished with very long bristles. The fan con- 

 sisted of a broad, moderately long, and posteriorly rounded 

 plate, and of two minute and simple longish-oval laminae, 

 likewise inserted on both its sides at the sixth joint of the tail ; 

 these laminae were only about half as long as the false feet of 

 the fifth joint of the tail. 



From the notices which I have here briefly communicated 

 respecting the development of some Decapods, it therefore 

 results that several of these animals, as first discovered and 

 described by Thompson, undergo a very considerable and 

 highly remarkable metamorphosis, after having thrown off 

 their egg-shells. I therefore confess that I have done Thomp- 

 son injustice in not putting faith in that discovery, relying on 

 the history of the development of the Cray-fish, and trusting 

 too much to analogies in the structure of full-grown Decapods ; 

 perhaps likewise led into error by the examination of very 

 small embryos of Eriphia spinifrons and of Palcemon Squilla. 

 It results, however, from the above communication, and 

 from the history which I have given of the Cray-fish (and 

 which I intend next spring partially to subject to a revision), 

 that different Decapods quit their eggs in a different stage of 



