196 



INVERTEBRATE MORPHOLOGY. 



nephr 



posteriorly to eiid usually in one or two cereal processes, 

 and anteriorly show a dilatation succeeded by a more or 

 less well-marked narrow region, the two giving rise to a 

 bead and neck. The body is covered upon the outside by a- 

 cuticle, which may be smooth as in the genus Ichthydium, or 

 take the form of overlapping scales as in Chcetonotus (Fig. 95), 

 sometimes bearing spine-like prolongations. Along the ven- 

 tral surface two bands of cilia run from 

 the posterior part of the head region 

 almost to the hind end of the body, 



*/ * 



and in addition to these patches of 

 cilia are found upon the ventral surface 

 and on the sides of the head, some of 

 which are undoubtedly sensory in func- 

 tion. Beneath the cuticular covering 

 lies the ectoderm in the form of a layer 

 of protoplasm in which no cell outlines 

 can be perceived, but which contains 

 numerous scattered nuclei. A pair 

 of longitudinal muscle-bands lie be- 

 neath the ectoderm on the dorsal sur- 

 face, and other bands traverse the 

 coalom in an autero-posterior direction. 

 Transverse and circular muscles are, 

 however, absent. A distinct coeloin is 

 present, the greater portion of which 

 FIG. 95.-Chtonotu8 maxi- ig occup i ec i } however, by the internal 



organs ; it is not lined with a peri- 

 toneal epithelium, nor are any mesen- 

 teries present. 



The mouth is situated at the an- 

 terior extremity of the body and opens 

 into a muscular oesophagus (a?), which 

 opens in turn into the cylindrical 

 stomach (t). To this succeeds a short intestine opening to 

 the exterior at the posterior extremity of the body. 



No blood vascular system is present, but the excretory sys- 

 tem consists of a single pair of much-convoluted tubes (nephr) 

 which terminate at one end in a closed ciliated " funnel," 



mus (after ZKLINKA). 

 eg = nerve-ganglion. 

 dr = glands. 



i = intestine. 

 in = longitudinal 



muscles. 



neplir =. nepliridia. 

 oe oesophagus. 

 ov = ovary. 



