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, 13 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 was the largest, the hinder, entirely 
covered by the dorsal shield, the smallest. Hach 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 {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 branchiz seemed as 
yet to exist. The small maxille and mandibule were similar 
in form to grown specimens of Hyas: the mandibule, for in- 
stance, had already a very long palpus. On the other hand, 
the antenne 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 
