36 DESCRIPTIONS OF FOUR DISTOMES. 



of 1 millimetre, a breadth of 0.4 millimetre, and a thickness of 0.28 millimetre. It 

 lies transversely or diagonally across the body, with its posterior end on the right 

 side. The oviduct is a short narrow canal 0.013 millimetre in diameter which leaves 

 the ventral surf-ace of the ovary near its anterior end and proceeds to the ootyp in 

 the centre of the shell-gland. The receptaculum seminis is a large sac about the size 

 of the ovary and is constantly filled with spermatozoa. It has also the shape of the 

 ovary and lies immediately posterior to it. Its duct is a narrow tube, similar in size 

 to the oviduct, which proceeds from the anterior surface and joins the oviduct. 

 The shell-gland is an extensive group of glandular cells situated between the ante- 

 rior ends of the ovary and the receptaculum seminis, and enveloping the proximal 

 portion of the uterus and also portions of the oviduct and the median yolk-duct. 

 Laurer's canal could not be found. 



The yolk-glands are extensively developed and are situated at the sides of the 

 body mostly lateral to the intestinal caeca. They consist of a number of distinct 

 follicles on each side and are joined by a longitudinal duct. The number of these 

 follicles varies from six to eleven on a side, and each follicle is made up of from five 

 to ten rounded glandular bodies. Most of the follicles are between the intestinal 

 caeca and the lateral edge of the body; the extreme posterior and anterior ones, how- 

 ever, may be situated in the centre of the body between the intestinal caeca. The 

 anterior and posterior portions of the yolk-ducts on each side meet ventral to the 

 receptaculum seminis and form thus the two transverse yolk-ducts. These ducts 

 meet near the median plane and form the median yolk-duct. This duct in a large 

 worm measures about 0.3 millimetre in length. It runs anteriorly to the ootyp. 

 About midway in its course it expands to form a small yolk-reservoir, the diameter 

 of which is 0.06 millimetre. 



The uterus begins its course at the ootyp, and passes first towards the hinder 

 end of the body. It proceeds, as a small and moderately straight tube, between the 

 testes to the space behind those organs, which it entirely fills with its numerous irreg- 

 ularly transverse folds. It then runs forward, winding in transverse folds between 

 the testes, filling the space between them and the receptaculum seminis, and passing 

 to the genital pore near the anterior end of the body. The uterus is thus very volu- 

 minous. It is filled with small dark-colored eggs which measure 0.039 millimetre 

 by 0.017 millimetre. No specialized metraterm is present. 



The following is a specific diagnosis of Ostiolum formosum. Elongated, flattened 

 worms. Length between 7 and 10 millimetres; breadth 1.5 millimetres; thickness 

 0.33 millimetre. No spines or scales are present. Oral sucker subterminal, 0.3 milli- 

 metre in width. Acetabulum sessile, minute, 0.07 millimetre in width. Pharynx of 



