89] LIFE HISTORY OF TREMA TODES—FA UST 89 



is in keeping with the studies of Odhner (1912), who points out the fundamen- 

 tal morphological relationship of the hermaphroditic species Liolope and 

 Haplometra to the unisexual BUharziella, Gigantobilharzia, Omithobilharzia, 

 and Schistosoma. 



The discussion leads to the conclusion that the furcocercous larvae possess 

 in common 1) a bifid tail, 2) a ventral sucker, 3) an oral suctorial pouch which 

 can be inverted, 4) a glandular esophagus without sphincter muscles, 5) 

 paired groups of salivary-mucin glands, four or more to the group, 6) multiple 

 testes, and 7) a specifically modified nervous system. In the light of present 

 knowledge all of these species fall within the limits of the family Schistoso- 

 matidae. 



Of all the known groups of trematodes the Holostomata have been the 

 group of least genetic study and most erroneous interpretation. On account 

 of their large size the adult holostomes have been known for many years and 

 dozens of species have been described. Nothing, however, has been known 

 of the parthenitae and their development. Without sufficient evidence 

 Brandes (1891:573) has interpreted the sketch of a miracidium of Strigea 

 (Holostomum) cornucopiae Molin (von Linstow,1877, Fig.30) as a metamorphos- 

 ing tetracotyle. In other words, Brandes concludes that the holostome has 

 a direct development without the intercalation of a parthenogenetic cycle. 

 Ercolani (1881:284-290; Tav. II, Figs. 16-22) has worked out the life-history 

 of Strigea erratica (Duj.) from the tetracotyle to the adult form, by infecting 

 Anas sp. with Tetracotyle typica cysts from the mollusk Planorhis corneus. 

 Altho Ercolani found a tetracotyle in a sporocyst (Tav. II, Fig. 18), he inter- 

 preted it as the invasion of the tetracotyle into the sporocyst of Cercaria 

 ocellata La. Ya\. Ssinitzin (1910:22, 23) has justly criticized Brandes' con- 

 clusion of the monogenetic development of holostomes, but in lieu of true 

 holostome evidence in support of the digenetic view he has substituted evidence 

 from Cercaria plicata, a peculiar distome larva which he has found to bear 

 certain relationships to the holostomes. 



It has been shown in this paper (p. 16) that there are parthenogenetic 

 cycles in Cercaria flabelliformis, a typical holostome, and that several genera- 

 tions of rediae are intercalated between the miracidium and the tetracotyle. 

 Thus, there is conclusive proof that the holostome has an alternation of genera- 

 tions, hermaphroditic and parthenogenetic, similar in kind to such alternation 

 in other Digenea. 



In spite of the strangely modified suctorial apparatus and posterior genital 

 organs of the holostomes, there seem to be good grounds for beUeving that 

 they originated from the distomes. They have an acetabulum, and frequently 

 the muscular rudiment of a genital pore just in front of the acetabulum (Fig. 

 52). On the other hand it is very doubtful if the lappets (Zapfenlappen of 

 Brandes 1892, Taf. 41, Figs. 5-15) bear any homology to the genital pore 

 rudiment. It has been shown, in fact, that the lateral lappets in Cercaria 

 flabelliformis arise from a pair of oval suctorial grooves (Fig. 41), and that in 



