i 1918 ^ 
TEANSACTIONS 
OF THE 
EOYAL SOCIETY OF SOUTH AFRICA. 
VOL. VII. 
MESTOMA ANTABCTICUM (sp. nov.) FEOM BLOEMFONTEIN. 
By T. F. Drbybr, B.A., Ph.D. 
Locality. — A small pond on clay soil near Bloemfontein. 
Size. — A very slender worm, tapering towards both ends, and, when fully 
extended, about 7 mm. in length and about 1 mm. broad. Five specimens 
were collected in November, and none of them contained eggs ; but after 
having been kept in the laboratory for two days two of them had a brick-red 
winter egg in each uterus. 
Description. — The anterior end can be withdrawn by special bands of 
muscle fibres, but it is not sharply set off from the rest of the body. The 
epithelium is not pigmented, the faintly yellowish-brown pigment being 
restricted to the mesenchyme. In the preserved specimens the body is 
roughly square in cross-section, the dorso-lateral ridges being, however, more 
distinct than the ventro -lateral ones. The two uteri simple, backwardly 
directed sacs. The mouth and the genital aperture open together. The pre- 
pharyngeal gut is appreciably shorter than the postpharyngeal portion. 
General. — From the above it will be seen that the present species is very 
similar to, one may almost say identical with, M. mutahile from Tierra del 
Fuego. This similarity is also shown in the structure of the reproductive 
organs. The testes are united posteriorly and also just in front of the 
pharynx ; each testis is a sacculated tube and is divided into an anterior 
and a posterior portion, since the tube contains no germ -plasm in the region 
immediately over the mouth. The two vasa deferentia are united into a 
short seminal duct. The only difference between the South African and the 
South American species seems to be in the structure of the oviduct and its 
receptaculum seminis. Bohmig (see v. Grraff, ' Turbellaria in Das Thierreich ') 
figures a long, thin oviduct with a laterally situated receptaculum, which is 
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