191 



LIFE HISTORY OF TREMATODES— FAUST 



19 



worth while to inquire into the facts and see if the outlined sequence of events 

 is always followed. In some cases the sporocyst is the mother of the cercaria, 

 in which case the redia cycle has been omitted. The accompanying table (III) 

 shows that of the fifteen species treated in this paper eight have cercariae 

 derived directly from the germ cells of the sporocyst. Of the seven remaining, 

 five are known to come from rediae, while the parthenitae of the other two 

 species of larvae are not known. 



TABLE m 

 GERMINAL EPITHELIUM 



Monostomata 



1. Cercaria pellucida 



2. Cercaria konadensis 



Holostomata 



3. Cercaria flabelliformis.... 



4. Cercaria ptychocheilus.... 



5. Tctracotyle pipieniis 



Distomata 



Xiphidiocercariae 



6. Cercaria crenata 



7. Cercaria glandulosa 



8. Cercaria diaphana 



9. Cercaria dendritica 



10. Cercaria micropharynx.. 



11. Cercaria racemosa 



Echinostome cercariae 



12. Cercaria trisolenata 



13. Cercaria biflexa 



Furcocercariae 



14. Cercaria gracillima 



15. Cercaria tuberistoma 



Types of development are characteristic of certain groups. The Mono- 

 stomata, Holostomata, and Amphistomata and usually the echinostome cer- 

 cariae develop within rediae. The xiphidiocercariae and the furcocercariae 

 arise from sporocyst tissue. A considerable modification of a typical life- 

 history, such as is found in Fasciola hepatica, is displayed among various groups 

 of Digenea. In 1835 von Siebold described a viviparous monostome larva 

 under the name of Monostomum mutahile, in which the miracidium bursts the 

 egg-shell while it is still within the uterus. Within this miracidiimi, without 

 any metamorphosis into a sporocyst, there develops a single redia. Schistosoma 

 japonicum has two sporocyst stages, of which the former is covered with a 

 smooth and the latter with a spinous integvunent (Leiper and Atkinson, 

 1915:202). This worm has no redia stage, for the cercariae develop within 

 the secondary sporocyst. Cercariae and rediae develop side by side in the 

 rediae of Cercaria flabelliformis. 



The sporocyst is much simpler than the redia. It is merely a sac with 

 ectoderm covering, and at times a secretory integimaent. Occasionally one 

 end is partially muscular. From the inner waU of this sac arise the germ balls 



