247] NORTH AMERICAN MONOSTOMES 29 



The excretory system of these worms cannot be fully made out in 

 preserved material and at most one can obtain accurate knowledge of only 

 a small part of this system without having had opportunity to study 

 developmental forms while living. In general the excretory bladder can 

 be made out in all species as a simple flattened sac, except in Cyclocoelum 

 elongatum, lying between the posterior arch of the intestine and the body 

 wall, usually closely approached on either side by the posterior extremities 

 of the vitellaria. It opens to the exterior on the median dorsal surface by 

 a small duct surrounded at its exterior opening by a strong sphincter. 

 Two main branches of the system open into the excretory bladder one on 

 either side. These branches follow in general the course of the intestinal 

 crura and are joined by many secondary branches which anastomose 

 freely forming a vast net-work ramifying the entire body. The ducts of 

 the system are composed of relatively heavy muscular walls which aid 

 in the movement of the excretory products toward the bladder. 



The nervous system so far as has been made out from the material at 

 hand does not differ materially from the description of Lang (1880). The 

 cephalic ganglia are situated one on either side of the pharynx and are 

 connected by a dorsal commissure which spans the anterior alimentary 

 organs between the pharynx and the sucker. In the miracidia are seen the 

 beehive-shaped eye-spots first observed by Van Beneden (1861) and later 

 described by Faust (1918). 



The vitelline glands in this family are very much alike in all genera 

 being composed of two main canals which lie parallel to and usually outside 

 of the intestinal crura. From these main stems side branches go out both 

 dorsally and ventrally. The glands are made up of small follicular bodies 

 arranged around the ducts so as to form grape-like clusters. The develop- 

 ment of these glands is constant within a species and may be built up on 

 the main stem with relatively few branches. The strongest development 

 of the secondary branches is found in Cyclocoelum microstomum and Cyclo- 

 coelum pseudomicrostomum and in the genus Hyptiasmus where the 

 branches of the vitelline glands form a net-work closely applied to the 

 intestinal crura. The vitelline substance is conveyed to the ootype by a 

 duct from each side in the region of the ovarian complex; these pass to a 

 point posterior to the shell gland where they unite. At the point of union 

 is usually found an enlargement, the vitelline reservoir. The duct then 

 passes to the dorsal side of the shell gland where it becomes embedded in 

 the latter organ; however, it emerges from this to re-enter it on the anterior 

 dorsal surface and just after its entry joins the oviduct at the point of its 

 enlargement to form the ootype. 



The cirrus pouch as stated by Kossack (1911) shows little variation. 

 It is a clubshaped muscular pouch containing a relatively large vesicula 

 seminalis to which unites a short weakly developed pars prostatica. This 



