3 so 



FRESH-WATER BIOLOGY 



68 (69) With a separate receptaaJum seminis, whose short duct is closed by a 

 muscular ring. Dermal rhabdites present. . . Strongylostoma. 



Only one species known in this country. 



Strongylostoma gonocephalum (SUliman) 1885. 



Length i-2 mm. Mesenchyma yellowisli, intestine 

 with yellowish oil droplets. Eyes carmine red. Small 

 rhabdites are present. This form differs from the 

 widely distributed European form, Strongylostoma 

 radiatum Miiller chiefly in the possession of two 

 shallow oval pits which lie close behind the eyes at 

 the side. The integument is sUghtly raised around 

 them and each bears vacuoles and rhabdoids. 

 Excretory pore opens into mouth. Erie Canal, 

 Monroe Co., N. Y. 



Fig. 621. Strongylostoma gonocephalum. {A) Entire 



animal: tr, tracts of rhabdites: M. pharynx; o», ovary; 



bs, bursa seminalis; vi, yolk glands; f, cirrus; go, genital 



pore; ec, egg capsule. X 40. (After Silliman.) (5) Out- line of anterior 



end with eye (a«) and shallow pit {sfi of one side. Enlarged. (After von 



Grafi.) 



69 (68) Without a separate receptaculum seminis Typhloplana. 



Only one species known in this country. 



Typhloplana viridata (Abildgaard) 1790. 



Length 0.5 to i mm. Transparent. Zoochlorellae in the mesenchyma give 

 it a grass-green color. Tapering at both ends. Without eyes. Anterior 

 end bluntly pointed, posterior end pointed. Pharynx just anterior to 

 center. Sexual pore close behind pharynx. Viviparous. The summer 

 eggs develop within the body of the parent. Winter eggs are as many as 

 ten in number and yellowish-brown in color. 



The pear-shaped bulbous cirrus contains a straight chitinous tube, the 

 ductus ejaculatorius. The male genital canal is set with small spines; the 

 small egg-shaped or somewhat elongated testes lie near or back of the pharynx 



Luther and von Graff regard the form collected from Monroe Co., N. Y., 

 and described by SiUiman luider the name of Mesostoma vimparum, also 

 those collected from West Twin Lakes and Old Channel Round Lake, 

 Charlevoix, Mich., and described by Woodworth under the names M. 

 viviparum and M . vividaiumy as identical with the European species. There 

 seems to be no doubt that this is the case. Typhloplana viridata was col- 

 lected by von Graff at Rochester, N. Y. 



Fig. 622. Typhloplana viridata. ^», Zoochlorellae; ^A, pharynx; (5 , 9>i°aleand 

 female genital pore; pe, cirrus. X 70. (After von GraS.) 



