1887.] 



ON CYCLESTHERIA HISLOPI. 



49 



In the following stage, represeuted Pl. VII, figs. 1—3, both 

 the vitelline membrane and the embryonic cuticle have been east 

 off, and all the appendages are freely exposed, though still exhib- 

 iting a rather imperfect development. The length of the embryo 

 in this stage is about 0,70 mm. The cephalic part has become 

 more produced, and its frontal edge, which in the preceding stage 

 formed a very slight and even enrve, is considerably arched in 

 the middle, so as to be sharply marked off both from the lower 

 and upper projections of the head, the former (L) being now 

 considerably produced and readily recognized as the labrum. 

 though still pointing almost straight downwards, the latter (x) 

 having assumed the form of a pivot-shaped process, issuing from 

 the upper plain surface of the head. The antennulæ (a 1 ) have 

 preserved their form and size nearly unchanged, whereas the 

 antennæ (a 2 ) have become considerably elongated, with the 

 branches nearly as long as the basal part, or scape, being still, 

 however, quite simple, without any trace of segmentation. The 

 mandibles (31) have retired to the posterior part of the cephalic 

 division and assumed their characteristic form and position, 

 though still separated ventrally by a rather wide interstice 

 (see fig. 3). Behind the mandibles, the two pairs of maxillæ 

 (rn 1 , ni 2 ) are very distinctly observed. The remaining part of 

 the body is somewhat fusiform, its hinder part being gradually 

 narrowed, with the extremity (T) somewhat exserted and slightly 

 bilobular, representing the first trace of the caudal plate. The 

 legs still exhibit a rather imperfect structure, and have not in- 

 creased in number. On the seven anterior pairs the edge is 

 distinctly lobular, showing the first trace of the epipodite, the 

 exopodite, and the endopodite, as also of the secondary lobes pro- 

 ceeding from the inner edge of the latter part. The two posterior 

 pairs, however, have still the form of simple transversal promi- 

 nences. The shell (C) has been partially detached from the sides 

 of the bod} T , and its dorsal portion is now distinctly defined. exhib- 

 iting inside a thickened rim, separated from the dorsal surface of 

 the body. It is, however, as yet quite small, obtecting but a very 

 restricted part of the body, and is not produced anteriorly and 



Vid.-Sehk. Forh. 1887. No. 1. 4 



