H. Rathke on the Metamorphosis of the Crustacea. 267 



branches at the two front pairs being somewhat longer in 

 proportion to the stem. On the fan of the tail likewise, con- 

 sisting of only one plate, the incisure is very deep, so that this 

 part is more distinctly divided into two flaps than in the 

 mature embryo of Pagurus. 



4. Hyas Araneus. — I obtained from Professor and Councillor 

 of State Reinhardt of Copenhagen, to whom I am likewise 

 indebted for the above-described young of Pagurus, several 

 specimens of a crab-like animal, which had been caught by 

 one of its possessors who had found a great swarm of them 

 in the North Sea : they were probably the young of Hyas 

 Araneus in two different periods of development. 



The smallest were, without their snout, 1^ lin. in length, 

 and were very similar to those Crustacea which Thompson 

 has already described as the young of a short-tailed crab. 

 The dorsal shield was moderately compressed from the 

 sides, and had in its hinder half a considerable height 

 in comparison to the breadth, so that it might in some 

 measure be compared to the shield of Daphnia. From the 

 upper side of it proceeded a thin appendage directed upwards 

 and backwards, which was about the same length as the 

 dorsal shield; but forwards and downwards proceeded a 

 simple and thin snout of about the same length. Of members 

 which might serve for swimming three pairs occurred ; and 

 of these, as in the above-described smallest larva or young of 

 Pagurus, the front pair w r as the largest, the hinder, entirely 

 covered by the dorsal shield, the smallest. Each of these 

 organs again consisted of a stem and two ramifications of 

 which the inner was almost cylindrical and composed of five 

 articulations, the outer one very compressed, and consisting 

 only of two articulations. Behind them were likewise five 

 pairs of legs, of which the front or largest was already pro- 

 vided with pretty far t developed pincers. Yet all the legs 

 were, in comparison to the two front pairs of joints for swim- 

 ming, exhibiting themselves as foot-jaws in a lower stage of 

 development, very small, and lay still completely hidden 

 under the dorsal shield. Not a trace of branchiae seemed as 

 yet to exist. The small maxillae and mandibular were similar 

 in form to grown specimens of Hyas : the mandibular, for in- 

 stance, had already a very long palpus. On the other hand, 

 the antennae had a form entirely different from those of full- 

 grown specimens; however, it would lead me too far were I to 

 describe these more minutely. The eyes were, in proportion 

 to the whole body, enormously great, and directed sidewards. 

 The tail was much longer than the cephalothorax, the snout 

 being left out of consideration, but was very narrow, and 



