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THE AMERICAN NATURALIST [Vol. LIII 



the life history of Fasciola hepatica, the sporocyst and redia 

 generations both occur, but in several groups, notably in the 

 stylet cercariae and the furcocercarise the redia stage has been 

 omitted or replaced by another sporocyst stage. 



Sporocysts and redia have not been sufficiently distinguished. 

 The sporocyst is an adult which has lost its digestive tube, while 

 a redia is an adult which possesses both a rhabdoecele gut and a 

 pharyngeal sphincter. In certain sporocysts the sphincter still 

 remains, as in C. dendritica. In other sporocysts, as in some fur- 

 cocercariae, while no definitely differentiated sphincter is pres- 

 ent, the anterior end of the sac is muscular, turning in and out 

 like the finger of a glove. This may easily be mistaken for a 

 rhabdoecele gut. 



The cercariae develop within the parthcnitae and usually at the 

 time of maturity break out of the parent and work their way 

 through the tissues of the host into the water. In case no suita- 

 ble host is at hand in which the larvae may continue development 

 they ordinarily encyst. Groups like the furcocercarise, however, 

 are not known to encyst. On the other hand, the writer has 

 found encysted larvae of C. hiflexa within the larval host and 

 encysted larva of C. micrapharynx even within the parent 

 sporocysts. 



The parthenitas of monostome, amphistome and holostome cer- 

 caria are redia;. Parthenitae of certain groups of distome cer- 

 cariae are sporocysts and of other groups of distome cercarise 

 are rediae, although some of the records are conflicting. This 

 shows the need of the accurate determination of the parthenita 

 of each cerearia, since the parthenita is a distinct generation in 

 the life history of the species. 



In order that the records may not be confusing the writer 

 proposes the name Cerearia gracilescens for C. gracilis O'Roke 

 1917, preoccupied by La Valette 1855, and G. minima for C. 

 minor Faust 1918, preoccupied by Lebour 1912. 



In conclusion, the effect of the larva on the mollusk must be 

 emphasized. It is an observable fact that heavily infected snails 

 die sooner than uninfected ones. The cause of this mortality is 

 both the mechanical disruption of the tissues of the infected 

 mollusk and the pathological changes within the cells of the in- 

 fected animal. A pathologieo-chemical study of this relation- 

 ship would be of great value to parasitologist and malacologist 

 alike. Ernest Carroll. Faust 



Univeksity of Illinois 



