1887.] 



ON CYCI.ESTHERIA HISLOPI. 



15 



pigment. The eye is moved by three pairs of very small muscles, 

 which on either side converge to a point located a little poste- 

 rior to that organ, beiDg here atfixed to the cuticle of the 

 head. 



At a short distance inferior, and somewhat anterior, to the 

 eye. the so-called oeéttus (figs. 3. 4, 5, or) is located. This pecu- 

 liar organ is very fully developed and scarcely at all smaller 

 than the eye itself. Viewed from the side (fig. 5, oc), it exhib- 

 its a somewhat triangular form. with the upper angle obtusely 

 rounded and the posterior somewhat more produced than the 

 anterior. It is encircled by a narrow zone of dark-red pigment, 

 the lateral surfaces being quite smooth and plain or very 

 slightly concave, and exibitiug an opaque whitish. colour as 

 also a peculiar iridescent lustre. Inferiorly and posteriorly, a 

 clear vaulted border is fonnd projecting from the corresponding 

 sides of the organ, each border exhibiting a miimte and regu- 

 lar cellular structure, the cellular corpuscles apparently lying 

 densely crowded side by side. Seen from above (fig. 3) or be- 

 low (fig. 4). the ocellus appears somewhat compressed. nar- 

 rowed in front, and gradually widening posteriorly and inferi- 

 orly. with the lateral surfaces obliquely upturned. 



From the anterior angle of the ocellus, a chord, apparently 

 of nervous nature, and containing a few r distinct cellular corpuscles, 

 passes to the dorsal edge of the head, immediately behind the 

 serrate part; and at a short distance behind the insertion of 

 this chord a small cup-shaped depression is observed, from which 

 a somewhat geniculate string, apparently of chitinous structure, 

 extends backward to the lower side of the compound eye. Another 

 very small cup-shaped depression (x), encircled by a thickened 

 rim. occurs farther back on the dorsal edge, at some distance 

 from the posterior projecting part of the cephalic crest, appa- 

 rently corresponding to the so-called „aflixing organ" in Limnadia, 

 but in the present Phyllopod quite rudimentary, except in the 

 embryos, where it is very dktiuct and pr<jjecting. 



The antennulæ (figs. 4. 5, a 1 ) originate on the inferior 

 side of the head, at the base of the labrum, their insertion thus 



