450 



FRESH-WATER BIOLOGY 



20(121) Two testes in each proglottid N emafo taenia Luhe iSgg. 



Strobila thicker near anterior end becoming thinner 

 and eventually filiform, circular in cross-section. Neck 

 short, cirrus-pouch long, passing within longitudinal 

 muscle layer. Vas deferens long, with ventral loop 

 between ovary and excretory canals. Two testes, 

 dorsal and symmetrical. Vitellarium almost exactly 

 in center of body. Ovary ventral, nearly median; 

 uterus horseshoe-shaped, breaks up early into numer- 

 ous capsules with 2 to 4 eggs, usually 3, in each cap- 

 sule becoming ultimately 13 to 30 small dark uterine 

 capsules. 



Records of its occurrence in'North America are open 

 to question. ' 



T>^e species. 



N ematotaenia dispar (Goeze) 1782. 



Fig. 761. Nematotaenia dispar. Transverse section of 

 ripe proglottid; c, cirrus; t, testes; m, retractor muscle of 

 cirrus; t'/, vitellaria; oi', ovary; vd,wa.s deferens; i', vagina. 

 Magnified. (After Fuhrmann.) 



121 (120) One testis in each proglottid. 



Cylindrotaenia Jewell 191 6. 



Strobila thickest near center, becoming thinner 

 towards both ends. Neck long. Single testis 

 round, on aporal side of proglottid just dorsal to 

 transverse diameter. Cirrus-pouch short, ending 

 at longitudinal muscle layer. Vas deferens short, 

 nearly straight. Uterus breaks up into capsules 

 each containing 4 to 6 eggs, becoming enclosed 

 later in two conical organs, one dorsal and one 

 ventral, which are large transparent uterine cap- 

 sules. 



Type species. 



Cylindrotaenia americana Jewell 1916. 

 Perhaps Taenia pulchella Leidy 1851 belongs 

 here. 



Fig. 762. Cylindrotaenia americana. Transverse 

 section of ripe proglottid; t, testes: vd, vas deferens; c, 

 cirrus; v, vagina; ov, ovary; vt, vitellaria. Magnified. 

 (After Jewell.) 



122 (i) Larval forms; reproductive organs undeveloped 123 



Usually small and unsegmented though some bladder-worms reach considerable size and 

 even show the beginning of proglottid formation. On the whole these larvae show little or no 

 organ differentiation and are distinguishable from adults by the absence of characteristic 

 structures. Most larvae are encysted but there are numerous free forms. 



123 (124) Four long proboscides covered with hooks. 



Very rare but easily recognized. 



Trypanorhyncha (p. 434)- 



124(123) No proboscides with hooks present 125 



125 (126) Scolex and sucking organs hardly differentiated at all and the 

 latter when present never more than two. 



Larvae of Pseudophyllidea. 



(See also Sparganum, p. 434.) 



The anterior end of these and other larvae is often rolled in so that its exact character is 

 difficult to determine. 



