198 CLASS VI. 



to the mother and carried about by her (BracJtionus, &c.) ; and thus, in the cold season 

 of the year, these animals are oviparous. 



Besides the male of Notommata anglica, discovered by BRIGHTWELL, that of N. 

 Sieboldii has been observed by LEYDIG, who further gives reasons for believing that 

 Enteroplca hydatina EHR. is the male of Hydatina senta, Notommata granularis the 

 male of Notom. Bratitiionus, and Diglena granularis the male of Dig. catcllina. 

 GOSSE also has ascertained that the sexes are distinct in many others 1 . The males 

 are less than the females, and also differ in form in most cases. The dioecious character 

 of the class may thus be considered to be established. 



The generative organs of the males consist of a white and round 

 bladder or testis, filled with spermatozoa, and an efferent duct 

 (penis DALRYMPLE) ciliated in the interior, which opens close to 

 the outlet of the respiratory vesicle. All the males observed are 

 entirely destitute of digestive tract; they possess the respiratory 

 organs of their species, whose function seems to suffice for the 

 maintenance of their short life, employed exclusively in impreg- 

 nating the females.] 



The nervous system has been discovered by EHRENBERO in 

 different genera, and he described, as central portion, different ganglia 

 (ganglia cephalica seu cerebralio^ situated close to the wheel-organ, 

 from which distinct nerves arise. In Hydatina senta, according to 

 the investigations of the same observer, two threads also arise from 

 them that run downwards on the abdominal surface, and unite to form 

 a ganglion from which a single nervous string with many small 

 ganglia or swellings arise 2 . As organs of sense, in most of them red 

 eye-spots (generally two, sometimes one or three, seldom more than 

 four) have been perceived; sometimes these exist in young individuals 

 alone, and disappear on full growth, as in the genus Floscularia. 



Besides the muscles of the special parts, there are found in many species thin 

 bundles of muscles running longitudinally, one on the dorsal surface, one on the 

 abdominal surface, and two lateral. 



With respect to the geographic distribution of Wheel-animalcules nothing deter- 

 minate can yet be specified. Only do we know, from the observations and notices of 

 EHRENBERG, that, besides Europe, they are found in northern and western Asia, in 

 the north of Africa and in North America. Beyond doubt they occur in all quarters 

 of the world. The physiological peculiarity of life suspended for a length of time, to 

 be again awakened by the vital stimulus of fluid, has given a special celebrity to these 

 animals. On this subject we refer to what will be offered below when we notice 

 Rotifer vulgar is, in which this phenomenon has been chiefly observed. 



1 [GOSSE On the dioecious charact. of the Rotifera, Proceedings of the Royal Soc. 

 Vol. vin. pp. 66, 68.] 



8 Die Infusionsthierchen, s. 416. Somewhat differently ordered is the nervous 

 system in Notommata (s. 425) and in Diglena (s. 443), but in all there lies a principal 

 mass, as the collection of nervous ganglia, on the dorsal surface of the anterior 

 extremity of the body. 



