43] LIFE HISTOR Y OF TREMA TODES—FA UST 43 



are preserved. Application of strong acid to the granule causes an evolution 

 of gas. The granules are negative to inorganic CO2 tests, and are non-crystal- 

 line, as determined by the petrographic microscope. They take hematoxylin 

 stains readily, altho they do not stain deeply. They give no Molisch reaction. 

 The xanthroproteic test is positive, indicating a benzene nucleus. It is 

 probable that they consist of a conjugate protein before fixation. Fixation 

 with mercuric chlorid alters them, since they are then acid and alkali re- 

 sistent. 



Generalizations on the excretory sytem. The excretory system of the 

 trematodes, including both cercariae and parthenitae, is essentially a bilateral 

 system. It arises as two paired tubules, which fuse in the bladder region of 

 the cercaria to form the vesicle. The mature system of the parthenitae is 

 highly modified from the primitive type. The system as found in the cer- 

 caria is carried into the adult without very profound modification. 



Most individuals of all generations contain within their excretory systems 

 spheroidal concretions, which are waste organic products, quite probably 

 derived proteins. They lodge in the main tubes and are expelled thru the 

 excretory pore. 



DIGESTIVE SYSTEM 



The most uniform system in the Digenea is the digestive tract. With the 

 exception of the sub-order Gasterostomata and the super-family Prostomata, 

 the enteric canal is triclad in character. The main features of difference in 

 the various families of the group is the modification of the esophagus region of 

 the gut. In most forms there is a pharynx sphincter just within the oral 

 pocket. In other species the pharynx is small and inconspicuous. In still 

 others there is no bulbus around the esophagus, but in its stead a group of 

 gland cells. 



The digestive system in the cercaria is not distinctly a larval system but 

 practically a fully matured system. In some cases it is not functional, as in 

 the Monostomata, where the paired ceca are still filled with a jell (Fig. 13) ; 

 in the Schistosomatidae there is the interesting phenomenon of short ceca in 

 some species {Cercaria gracilUma) and entire absence in others (C tuheristoma) . 

 While the larval digestive glands of the cercaria may not be retained or may be 

 metamorphosed in the mature worm, nevertheless they are functional in 

 most larvae. 



The forking of the ceca is not constant, varying in different species. Even 

 the relative length of the parts of the tract varies greatly in the same individual 

 at different times, due to the extreme limits of contraction and expansion of 

 the larva, so that this relation of parts can not be entirely depended on as a 

 basis for diagnosis. As a whole the digestive tract is remarkably uniform and 

 simple, which might be expected in a larva in which the food supply is so 

 accessible. 



The sporocyst has no digestive tract, but takes its nourishment directly 

 thru the body wall. In consequence the cells of the epidermis are thin and 

 at times apparently glandular, as in the stylet cercariae. 



