308 BULLETIN OF THE 



The appendages back of the mandibles now appear in regular suc- 

 cession in the form of hyaline pi'otuberances from the opaque yelk. 

 Four days after the gastrula-stage (PL I. Fig. 3), the embryo has the 

 form portrayed on Plate I. Fig. 4. 



The rudiments of the appendages have appeared as far back as the 

 sixth pair (first pair of maxillipeds). The second pair of antenna? (PI. 

 I. Fig. 4, II), are now double appendages, the two parts representing 

 the flagellum and scale of the future antenna. The appendages behind 

 the mandibles are bilobed from the time of their earliest appearance. 

 The labrum (I b) has moved backward, so as now to lie on a line with 

 the second pair of antennae. 



The antenna? rapidly increase in length, assuming the form of ribands 

 which lie along the outer side of the following appendages, parallel with 

 the abdomen. Three days after the stage last described they reach as 

 far back as the first pair of maxillipeds (PL I. Fig. 5). The first pair 

 (I) lie on the outer side of the second pair (77), and are slightly shorter 

 than these. The outer branch of the second pair, again, is a little 

 longer than the inner branch. Even at this early period traces of seta? 

 are seen on the extremities of both pairs of antenna?. The rudiments 

 of the appendages are now formed as far back as the third pair of max- 

 illipeds (PL I. Fig. 5, VIII), the abdomen (a b) extends forward so far 

 as to meet the labrum (I b), but is still unformed along the median dorsal 

 line. Some scattered blotches of a dark color (o c) are the first indica- 

 tions of the pigment of the compound eye.* 



On the following day (Aug. 5) I observed the first appearance of the 

 median simple eye in the form of a black pigment-spot in the middle 

 line of the head. 



The embryo gradually encroaches upon the unabsorbed yelk-mass on 

 the dorsal side of the egg. The outline of the carapace (PL I. Fig. 6, 

 cp, four days before hatching) comes into view, extending posteriorly 

 beyond the third pair of maxillipeds. Under the posterior part of the 

 carapace the heart appears as a transparent pulsating sac (k t). The 

 abdomen (a b) becomes divided into segments by transverse constrictions 

 which begin on the ventral side, the side which is applied to the ventral 

 face of the cephalo-thorax of the embryo. Within the abdomen are 

 seen the ganglia of the nervous system (PL I. Fig. 6, ug). The end of 

 the abdomen is produced into two blunt lobes, on the borders of which 

 the seta? are already visible. 



* The development of the eye certainly lends no countenance to the view that its 

 stalk is an appendage homologous with the antenuae, etc. 



