MUSEUM OF COMPAEATIVE ZOOLOGY. 309 



Plate I. Fig. 8, represents an embryo further advanced. The abdo- 

 men has lengthened to such an extent that it entirely conceals the 

 labrum, and extends forward so as to almost meet the tip of the rostrum 

 (r s), which lies bent beneath the head. The maxillipeds have increased 

 in length, and extend forward as two-branched appendages on each side 

 of the abdomen. At the base of the rostrum is the simple median eye 

 (ocl) ; the permanent eyes (o c) show through the egg-shell as oval 

 black spots. 



In the still older embryo in the egg represented on Plate I. Fig. 9, 

 the unabsorbed yelk (v t) has so diminished as to appear as a large 

 greenish patch on the dorsal side of the embryo. The whole margin of 

 the carapace is clearly denned, and its posterior or cardiac portion is 

 unobscured by underlying yelk. The eyes (o c) now form two black round- 

 ish spots at the anterior end of the embryo, so large that they are very 

 conspicuous to the naked eye. The corneae and cones are now formed, 

 and the eye is thrust out a little upon a very short stalk. The antennae 

 of the first pair (/) are divided into two segments, a long proximal and 

 a short oval distal one. The latter is furnished with a few seta? at its tip. 

 The two branches of the second antennae (//) are also tipped with setae. 



In the course of the development of the embryo within the egg, 

 the egg has become larger than it was when first laid. A few hours be- 

 fore hatching (PI. I. Fig. 10), it measures 1 mm. in long diameter. A 

 small patch of yellowish green (vit) just behind the eyes is the only 

 remnant of the unabsorbed yelk. The abdomen (a b) has lengthened to 

 such an extent that it reaches far beyond the mouth, between the eyes, 

 to the dorsal side of the head. The basal segment and the two branches 

 of the second pair of antennae are now clearly defined, and have acquired 

 very nearly the form which they have in the larva after hatching. The 

 maxillipeds have grown to a very large size, and conceal the oral ap- 

 pendages in front of them. 



Embryos removed from the egg an hour before hatching (PI. I. 

 Fig. 11) disclosed two pairs of two-branched sac-like appendages (Figs. 

 11, 13, IX, X), concealed between the bases of the third maxillipeds. 

 These are the rudiments of the two pairs of chelipeds of the adult 

 prawn. The structure of the embryo is now the same as during the 

 first larval stage. 



First Larval Stage (PI. I. Figs. 14-18; PI. II. Fig. 1). — When it 

 first issues from the egg the young prawn is 2J mm. in length. The 

 carapace is broad, produced between the eyes into a long, pointed ros- 

 trum. At the base of the rostrum is a small simple eye. The com- 



