45 233 



three to six vibratile tags; a conti-actile vesicle is hardly ever observed with cerhiinly 

 (Cyrtonia: Rousselet). The testis is formed as in most of the rotifers; prostata friands 

 are ahnost always present; the ductus seminalis opens upon one of the Hrst fool 

 joints; commonly it is the same organ which when turned inside out is used as 

 penis. Only in the ßzc/Ze/m-species do we find a highly complicated structure, a real 

 penis differing much from what we commonly find among the Rotifers. The muscle 

 system seems in tlie whole family to be of a very conform structure; it is always 

 highly developed, especially the transversa] muscle bands are very conspicuous and 

 are present in a number from five to seven. Conglomerates of opaque corns are 

 almost always observed over the testis. Two foot glands seem always to be present. 

 As far as I have seen, most of the males of Notommatidœ are almost just as slowly 

 creeping or slowly swimming animals as the females; onlj' the males of Dlglena are 

 vigorous swimmers. They are difficult to detect, many of them resembling young 

 females. For that very reason I suppose they are so rarely observed. 



Hydatinidæ. 



The family Hydatinidæ, as I understand it, comprises only three genera Hyda- 

 tina with H. senta, Rhinops with R. vitrea and Notops with A'^. brachioniis. Of all 

 the three species tlie males are known; that of N. brachionus ho^Never only slightly. 

 Best described of all Rotifera males is that of H. senta. 



Hydatina senta Ehrbg. 



Male: Ehrenberg: 1838 p. 412. 

 Ley dig: 1855 p. 98. 

 Colin: 1856 p. 435. 

 - 1858 p. 284. 

 Leydig: 1857 p. 410. 

 Plate: 1886 a p. 36. 

 Weber: 1888 p. 42. 

 Female: de Beauchamp: 1909. 

 Martini: 1912 p. 425. 

 Tab. VIII, fig. 1—2; Tab. IX, fig. 1—6; Tab. X, fig. 3—4. 

 As well known the female, anatomically as well as biologically is one of the 

 best studied Rotifera of all, especially owing to the admirable investigations of de 

 Beauchamp (1909) and Martini (1912 p. 425). 



As mentioned above the male was already described by Ehrenreug but as 

 a special form: Enteroplea hydatina; Leydig, Cohn, Plate and Weber have all 

 contributed to the study of its anatomy. It was my intention to use Hydatina as 

 the main form on which to base all my studies of the males of Rotifera. The male 

 was found in 1901 in a single pond; this was filled up and I did not see the male 

 again before 1920. According to my experience H. senta is restricted to very slowly 

 outdrying pools, polluted by outfiows from dung-hills; further it is only to be found 

 in the early spring. Of these two points I had no clear understanding before the 

 spring of 1920. 



