386 T. B. ROSSETER ON HOLOSTOMUM EXCISUM, AND THE DEVELOPMENT 



"The acetabulum, or mouth-sucker, is 0*15 mm. in diameter; 

 continuous from this is a bowl-shaped phaiwnx and the intestines. 

 The ventral sucker lies distally in the middle of the head cavity, 

 and has a diameter of 0'31 mm. The cavity or cleft of the head 

 is j)ractically filled with these two suckers, which are joined 

 together by a muscular belt (or, as von Linstow calls it, a bridge). 

 Each of these suckers possesses a spur-like protuberance.* Two 

 long muscles which commence at the dorso-anterior portion of 

 the head continue their course (on either lateral border) to the 

 extreme posterior end of the body. 



'' There are two large testes, one anterior and one posterior. 

 The shell gland, which is nearly square, divides the two testes and 

 spreads itself out anteriorly and posteriorly of them. The vesi- 

 cula seminalis is a winding duct situated behind the posterior 

 testis, but anterior of the stoma of the uterine aperture. 



" The receptaculum seminis is pyriform, and is situated dorso- 

 median (in the body parenchyma), on the posterior side of the 

 ovarium. The vitellaria runs the whole length of the creature 

 from the head to the tail, and is located more especially on the 

 ventral side.f The ductus vitellus runs between both testes, and 

 is covered by the shell gland. 



" The orifice of the laurer canal is posterior to the ovary — 

 keimstock — on the dorsal side. Its lumen is Q'016 mm. in length, 

 and one /x in breadth. The oviduct makes a junction with the 

 shell gland dorsal of the intestine, and runs along the ventral 

 side of the anterior testis. 



" The uterus has a short ascending and a long descending duct. 

 It is connected with the shell-gland, and its tract lies through 

 the posterior portion of the body. It then runs ventrally and 

 terminates distally in the uterus bowl or cylinder. This cylinder 

 is a muscular tube perforated through the middle of the canal, 

 and surrounds the body wall in the form of a preputium. It 

 occupies one-fifth of the posterior portion of the body. The 

 eggs are golden-coloured, (HO mm. long and 0*075 — 0*078 mm. 

 broad." 



* Von Linstow makes no mention of a lobe or gland which I find at the 

 terminative end of each spur. 



fin my specimens of //. cxcisum and other species of Holostoniidae, I 

 find that the vitellaria is confined to the arched posterior portion of the 

 body and lies dorsally and ventrally. 



