358 MEMOIRS OF THE NATIONAL ACADEMY OP SCIENCES. 



The larva, immediately after hatching, is shown in side view in PI. xiv, Pig. 3; in ventral view 

 in PI. xv, Fig. 8, and in dorsal view in Fig. 7 of the same plate. The carapace is nearly half as 

 long as the entire animal, and its posterior border, which is deeply emargiiiated, crosses the midde 

 line over the posterior edge of the tenth somite; the somite which carries the appendages which 

 are usually called, in the decapod Crustacean, the second pair of legs. There is a short, rather 

 stout rostrum, and the anterior end of the carapace, which covers about half the eyes, is nearly 

 semicircular. The posterolateral spines are short and curved outwards; there are no secondary 

 spines external to their bases, but there is a small median dorsal spine on the posterior edge of the 

 carapace, while the anterolaterals are absent. The antennule consists of a two-jointed shaft witli 

 two flagella, one terminal and the other arising from the dorsal surface of the distal joint of the 

 shaft. The antenna consists of a rudimentary exopodite, which is cylindrical and ends in five 

 swimming hairs, although it is of little use in locomotion. The large eyes are subspherical, 

 nearly sessile, and they touch each other on the middle hue dorsal to the autenuules. The man- 

 dibles are enormous ajid the two pairs of maxilla' rudimentary, as are also the first pair of inaxil- 

 lipeds, while the second pair, the large raptorial limbs of the adult, are well developed, although 

 the dactyle is not folded backwards upon the penultimate joint or propodite. The third, fourth, 

 and fifth maxillipeds, corresponding to the third maxillipeds and first and second ambulatory 

 limbs of decapods, are rudimentary, and the three following appendages are absent, although all 

 the corresponding somites are indicated as well as their ganglia. The abdomen is about twice as 

 wide as the thoracic region and somewhat more than half as wide as the carapace. The first five 

 somites are distinct and all end in acute posterolateral angles. The suture which separates the fifth 

 from the unsegmeuted region, which represents the sixth and the telson, is obscure, and this 

 region is longer than wide. 



The abdominal appendages gradually decrease in size from the first and largest to the fifth 

 pair, but all have their adult structure, except that they carry no gills and all are functional. 

 The telsou has four marginal spines on each side. Its posterior edge is slightly notched and car- 

 ries seven or eight pairs of minute movable spines. The newly hatched larva.- swim actively about 

 by means of their abdominal feet, not by Hexing and extending the abdomen, and notwithstand- 

 ing the presence of a great mass of food yolk in the walls of the stomach they eat voraciously. 

 By a lucky chance I found their proper food at once. Several bunches of the eggs of some 

 unknown Nudibrauch were in the aquarium in which the first brood hatched, and the larvre, nearly 

 a thousand in all, soon settled down upon them, covering them completely, and at once began 

 tearing them off and eating them. When washed awav from" them by means of a jet of water they 

 swam about the aquarium for a short time, but soon settled down upon the eggs again. As these 

 eggs are not very abundant they can hardly be the only food of the young larvie, although I could 

 find nothing else that they would touch, and they refused the eggs of all other Nudibranchs. At 

 this stage the heart consists of a large anterior chamber in the region of the second maxillipeds 

 and a large dorsal vessel tunning as far as the fifth abdominal somite, with a pair of ostia in each 

 somite. 



After about sixty hours they moulted aud assumed the form which is shown in side view in PI. 

 xiv, Fig. 4. The rostrum aud the spines on the posterior border of the carapace have lengthened, 

 but its shape and relative size are about as before. The second antenna; are more clearly divided 

 than before into a shaft and a scale, which has lost its hairs aud is more flattened. The first pair 

 of maxillipeds have made their appearance in the adult form, and the second pair are much larger 

 than before, and the dactyle is now folded back onto the edge of the flattened penultimatejoint. In 

 all other respects the larva is like the younger one, but a little longer and with less food yolk. In 

 about a week after hatching they molted again aud passed into the third (Kriehthus) stage, which 

 is shown from above in PI. xv, Fig. !>, and in side view in PI. xiv, Fig. 5. The rostrum is now greatly 

 elongated and reaches to the tips of the antennules. Small anterolateral spines have made their 

 appearance, as well ;is a small spine external to the base of each posterolateral. These latter are 

 greatly elongated aud very slightly divergent. A great change in the shape of the carapace has 

 taken place, as will be seen by comparing Fig. 7 of PI. xv with Fig. it. Its lateral margins are 

 nearly parallel, aud its greatest width only a little exceeds that of the abdomen. Its posterior 

 border is now nearly transverse and crosses the middle line above the last thoracic somite. The 



