MOEPHOLOGT OF CYCLOPS. 19 



which is crescentic (the convexity anterior) ; posteriorly separated by a median cleft. Each 

 valve forms a right-angled triangle, with rounded sides and the right angle posterior and 

 internal ; outer angle slightly produced and hearing three plumes, the innermost coarsest, 

 the intermediate smallest in every way, the outermost longest. 



Muscles of the liudimentari/ Feet. — In the fo/tale these consist of two sets : the one of 

 a number of slips taking origin near the anterior edge of the segment and converging 

 like a fan to l)e inserted at a slightly lower level into the base of the limb ; the other, 

 crossing this obliquely, consists of a few slips taking origin a little ventral to the former, 

 which it crosses on the inner surface and is inserted on the distal side of the vulvar slit. 

 The former probably closes the genital valve and would be its depressor. Possibly what 

 I have described as the attachment of the latter may be its insertion, in which case it 

 would raise the genital valve by leverage on the proximal end ; or it may rectify the 

 curve of the spermathecal duct described below*. 



In the male a small slip, very difficult to see, runs from the outer side of the segment, 

 about its middle, obliquely inwards to the ventral wall of the limb, and is doubtless a 

 lecatov. 



Histology of the Integument. 



The chitiiwus cuticle forms everywhere an investment to the animal, and is continued 

 inwards to the mouth, gullet, and fore part of the stomach, into tlie kidneys and into the 

 rectum. The processes it bears have been already noticed. Its thickness varies greatly, 

 being at a maximum in the shaft of the mandi1)le and the inner arthrodial ridge, at a mini- 

 mum in the arthrodial membranes; its consistency varies from complete flexibility to strong 

 rigidity and brittleness, but it is nowhere calcified. In sections of the inner arthrodial 

 ridge alone have I seen traces of lamination. It is everywhere underlain by a hypoderm, 

 except perhaps at the insertions of the muscles, which in some cases, at least (muscles of 

 the gullet), appear to rest directly on the cuticle. The cuticle is readily traversed by 

 even dilute acids. 



Hijpodevm. — This is composed of polygonal, mostly hexagonal, nucleated cells. In 

 the living state neither nucleus nor cell-boundary is seen, only a smeai'y-looking vacuo- 

 lated syncytium, in which, however, the existence of nuclei is readily demonstrated by 

 drawing a little weak acetic acid (one per cent, or less) under the cover. The oval 

 nuclei then come cleaidy into view. They have no exceptional features, and like the 

 connective-tissue nuclei, which they mucli resemble, show, when well stained, a reticulated 

 structure. The continued action of the acid determines a shrinking of the hypoderm 

 from the cuticle, as mentioned above. Nuclei are of rare occurrence in hairs and spines. 



The only successful demonstration obtained of the boundaries of the hypoderm cells 

 has been by the action of silver nitrate. For this I wash a few live animals in a filter 

 with distilled water, put them in distilled water in a watch-glass and add a few drops 

 of the silver solution (one per cent.) ; after about twenty minvites' I wash in distilled 



* We must note that this limb, at the base of which the genital opening is situated, corresponds exactly in this 

 respect with the sixth limb behind the second maxillie of the female Leptostraca and Malacostraca, a coincidence 

 found in no other Entomostraca than the Copepoda. 



3* 



