391 LIFE HISTORY OF TREMA TODES—FA UST 39 



hand the needs for a muscular enlargement sometimes cause the musculariza- 

 tion of the cornua (C. dendritica, Fig. 81; C. crenata, Fig. 55; and C. racemosa, 

 Fig. 100). In C. diaphana (Fig. 76) the modification of structure has taken 

 place before the enlargement of the long median vessel and the lateral tubes. 



The capillaries tributary to the lateral tubules are represented in their 

 most simple form in C. micropharynx. The internal anterior vessel may 

 move forward, as in C. crenata, or become rudimentary, as in C. glandulosa. 

 The external anterior tubule is usually the most fully developed. 



It is important to note that the lateral systems of the xiphidiocercariae 

 never anastomose or coalesce in any way. Thus the median sagittal plane 

 acts as a "watershed." 



In the forms studied no large flame cells were found in the course of the ex- 

 cretory system. If any minute flame cells were present they were concealed 

 by the thick integument. 



The literature shows a paucity of observations on the flame cells of larval 

 and adult distomes. Ssinitzin (1905) shows the details of the flame cells 

 in Gorgordera pagenstecheri and in Phyllodisiomum folium. They consist of an 

 ameboid cytoplasm in which is imbedded a spheroid nucleus with rich chro- 

 matic inclusions. This cell is the terminus of the capillary (cl). It is ordi- 

 narily funnel-shaped, but when distended becomes deeply reniform. The 

 junction of the flame cell and the capillary is marked by a considerable number 

 of cilia which vibrate rythmically, giving rise to Ssinitzin 's characterization, 

 "vibratile tip cell of the excretory system." 



A detailed study of the flame cell of the adult distome is given by Looss 

 (1896:110; Figs. 72, 77) for Distomum sanguineutn Sons. The details of the 

 cell per se are not appreciably different from those given by Ssinitzin, but 

 the distribution of the flame cells thru the body of the distome is described. 

 There are four symmetrically paired groups of three cells each in the middle 

 of the body, and one pair of two cells each in the anterior and posterior reaches 

 of the body, making sixteen pairs of flame cells and capillaries in all (Fig. 77). 

 This probably gives an indication of the arrangement of the flame cells in the 

 typical distome. In Distomum isoporum (Looss, 1894, Fig. 103) six paired 

 groups of ultimate tubules are figured with four flame cells to each group, 

 making forty-eight flame cells in all. In Distomum cylindraceum (Fig. 163) 

 there are six paired groups of capillaries with three flame cells to each group, 

 totalling thirty-six flame cells. Thus the number of flame cells is not constant 

 in different species but ordinarily remains constant for each species. 



Looss (1894:249, 250; Fig. 186) suggests that the fundamental larval system 

 is the fundamental system of the adult. Extension and modification occur 

 thru a dichotomy of the existing capillaries and flame cells, and an encroach- 

 ment of the tubules upon the capillaries. The greatest modification takes 

 place during encystment, altho this is in no sense a metamorphosis. 



Among adult American distomes the excretory system of Microphallus 

 opacus Ward alone has been worked out with the exactitude of the Euro- 

 pean workers (Wright, 1912, PL 17, Figs. 1, 2). This form has the distome 



