1887.] 



ON CYCLESTHERIA HISLOPI. 



51 



and the tail, being however still unsegmented. At the extremity 

 of this part, a pair of pointed projections occur, separated in the 

 middle by an angular incision (see fig. 4, T\ and immediately 

 above them another pair of much shorter projections are observed, 

 the former representing the caudal claws, the latter the last pair 

 of dorsal spines. Moreover, at some distance from the tip 

 on the dorsal side, two small bris ties have made their appear- 

 ance, easily recognized as the candal setæ (see fig. 5). The 

 legs are now much more fully developed, exhibiting all their 

 principal parts (see fig. 6), but still with very faint traces of the 

 marginal setæ and having the exopodite but very slightly produ- 

 ced upwards. Their number has increased to fourteen pairs? 

 but the four last are still imperfectly developed and densely 

 crowded together (see fig. 5, p u — p 14 ). The shell has increased 

 considerably in size and assumed a mor distinctly bivalved 

 form, though still obtecting only the six anterior segments of 

 the trunk, together with the maxillary and part of the mandibular 

 segment, the legs being still projected beyond its edges. It 

 exhibits, seen from the side (see fig. 5), a rounded form, with 

 the dorsal edge well-nigh straight, whereas the free edges are 

 evenly curved and join the dorsal edge at an obtuse angle 

 both anteriorly and posteriorly. Viewed from above (fig. 4), it 

 appears slightly compressed, exhibiting at each extremity in the 

 middle an angular incision, the posterior being the deeper. In 

 the anterior part of the shell, on each side, the insertion of the 

 adductor muscle is easily observable, as also the shell-gland (see 

 fig. 5 gl). Of the inner organs, the intestine may now be dis- 

 tinctly traced running along the axis of the body, being however 

 partly concealed by the remnant of the yolk, which forms two 

 rather narrow masses, extending on each side of the intestine 

 from the adductor muscle of the shell backwards, and gradually 

 disappearing at some distance from the posterior extremity. 

 Above the intestine in the anterior part of the trunk, moreover, 

 the heart is developing, and exhibits already slight contractions. 



The stage represented fig. 7, from the right side, is much more 

 fully developed, and in the general form agrees rather with the 



4* 



