Report on Larval Crabs. 5 



First Young Stage. 



The ci'ab which resulted from the moulting of the Megalops is shown in 

 fig. 13. The cephalic region is of a beautiful blue colour ; the pigment con- 

 sists there of minute yellow spots. Over the hepatic and cardiac regions 

 these little yellow spots are present, but fewer in number. The digestive 

 track is coloured dark broAvn. 



Colours after Preservation. 



The bright colours vanish with preservation. A certain amount of pig- 

 mentation persists, however. Some larvte which had been preserved in 

 formaline solution for ten years were examined. The protozoea shows 

 brown eyes, and pigment of that colour internally dorsal to the maxillipedes. 

 Brown pigment is also present in the abdominal segments, a prominent 

 amount being visible in the last segment. 



Zoese which, when alive, had blue eyes, green and brown pigment, with 

 luminous yellow on the outside of the eye, were, after preservation, coloured 

 as follows: — The retinal region of the eye was a brown ball. Brown 

 pigment was present on the anterior side of the eye-stalk, on the base 

 of the antennules, in the mouth region, and along the ventral surface of 

 the abdomen. Similar pigment was present in the dorsal surface of the 

 last abdominal segment ; there (at the anus) the ventral pigment extends 

 to the dorsum. In the other segments the pigment is slight on the dorsum. 



The pigmentation of the preserved Megalops is similar to that of the 

 Zoea, viz., brown. It is present in the body, eyes, and the abdomen. In 

 one specimen the brown pigment was almost entirely gone. This Megalops 

 had evidently been dead some time before being preserved. A crab of the 

 first young stage exhibited dark brown pigment in the eyes and a lighter 

 brown or amber colouration in the central portion of the cephalothorax. 

 The latter pigment is seen both from the dorsal and ventral sides. A 

 little brown colour was observed in the abdomen about the middle of 

 its length. 



Structure of Larvce. 

 Protozoea. 



The protozoea is the I. Zoea confined in a delicate sac which is prolonged 

 into plumose digitate processes at the anterior and posterior extremities. 

 The covering shows no segmentation into cephalothorax a,nd abdomen. 

 The I. Zoea issues from the protozoea not as the result of a regular moult, 

 but through the rupture of this skin. 



Faxon,* in several instances, observed some of the terminal digitate 

 processes invaginated just as were the spines of the I. Zoea. He con- 

 sidered that all these processes were invaginated while the larva is in the 

 egg. " The cuticle is not conformable to the underlying Zoea integument, 

 as it has neither dorsal nor frontal spines, and the antenna and tail are 

 very different." This author found that the protozoea of Oarcimos mcenas 

 remained unchanged in confinement for 24 hours. Meanwhile, it 

 increased to such a degree that the delicate investing membrane was no 

 longer ample enough for the enclosed Zoea, and the first exuviation took 

 place. The cuticle of the abdomen was cast oft in one piece, and the telson 

 was used for removing the remainder of the covering. The cuticle was 

 ruptured over the dorsum of the cephalothorax by the dorsal spine 

 erecting itself. 



* Faxon: " On Some Points in the Structure of the Embryonic Zoea." Bull. Mus. 

 Comp. Zool., Harvard, Cambridge, Mass., Vol. VI., No. 10, 1880. 2 plates. 



