Helminth Fauna of the Dry Tortugas. 



31 



Dimensions of one flattened: Length 2.17; breadth 1.08; diameter 

 of oral sucker 0.23; pharynx o.ii; ventral sucker 0.50; ova, exclusive 

 of filament, 0.054 by 0.027. 



Helicometra execta sp. nov. (Figs. 34-39.) 



Body variously shaped, linear, oval to pyriform; ventral sucker 

 from 1.25 to twice the diameter of the oral sucker; pharynx subglobular, 

 preceded by a very short prepharynx ; esophagus relatively long ; intes- 

 tinal rami extend to near the posterior end; genital aperture median, 

 at bifurcation of the intestines; cirrus-pouch cylindrical, median, or its 

 posterior end deflected to the right. In any case the principal length 

 of the cirrus-pouch is in front of the ventral sucker; prostate represented 

 by many cells which surround the ejaculatory duct. Testes variable; in 

 some specimens they were not present; in others they were represented 

 only by loose aggregations of testicular cells, as if the organ was almost 

 spent. In those individuals in which testes were present there was little 

 uniformity. In some there was but one testis, which corresponded in 

 appearance and position with the left anterior testis of Helicometrina 

 nimia. In other cases (figs. 38a, 38^^) there was a single median testis 

 immediately behind the ovary. In others no testis was present (fig. 38c). 

 This figure was drawn from the ovary of one of the largest mounted 

 specimens in my collection, 2.45 mm. in length. The specimen is stained 

 and mounted in balsam and shows the details of structure very well. 

 The testes have entirely disappeared. The ovary is lobed ; usually 4 or 5 

 lobes can be made out. It lies transversely about half-way between the 

 ventral sucker and the posterior end. Anterior and dorsal to the ovary 

 is a transversely placed yolk-reservoir which receives ducts from each 

 side, and dorsal to this is the seminal receptacle. The shell-gland lies 

 on the anterior and dorsal border of the ovary. The vitelline glands are 

 diffuse, posterior, and marginal, and extend forward about to the pharynx. 

 Behind the ovary they tend to form 4 parallel, longitudinal rows, the 

 2 on one side of the median line being separated from each other by the 

 intestine, and the 2 median rows having the excretory vessel between 

 them. The wreath-like folds of the uterus lie between the ovary and 

 the ventral sucker. Each ovum is provided with a long filament and 

 their arrangement in the uterus is similar to that of Helicometra torta. 

 The excretory vessel is inconspicuous in the mounted specimens. It 

 appears to be essentially like that of the preceding species. 



Following are measurements of specimens mounted in balsam: 



I. From Hmnulon plumieri. 



