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The body of the Rotifera females is commonly described as consisting of 

 three parts, an anterior part carrying the wheel-organ and mouth and enclosing the 

 brain and retrocerebral organ, the middle part containing the viscera, and finally 

 the foot. It is covered by a cuticula which, in the middle part, is often thickened 

 to a lorica in which head as well as foot may often be drawn in; where a lorica 

 is wanting, the body is commonly more or less segmented or as in the sessile fa- 

 milies, where the three main parts of the body are not distinctly separated from 

 each other, highly contractile. Besides, the body of the females is characterised by 

 the most extraordinary variation, relating to the shape of the body, the form and 

 composition of the lorica, the thickness of the cuticula, the development of the 

 foot, and the shape of the disc and the wheel-organ. This great variation is developed 

 in a much slighter degree in the males of the Rotifera. 



Firstly sessile male Rotifers are hitherto wholly unknown and most probably 

 do not exist, all males belonging to sessile females being conical without any con- 

 spicuous differentiation of the body; the cuticula is always extremely thin, much thinner 

 than in the female and therefore also very hyaline. In the more primitive families, as 

 especially the Notommafidce, where the body is conspicuously segmented and more 

 or less telescopic, the segmentation in the males, especially in Diglena, in some spe- 

 cies of Notommata, and perhaps also in Copens, is often rather obvious, but the 

 telescopic power is much smaller; f. i. C. labialus and C. pachyurus in the female sex 

 can telescope themselves in such a way that the body is ballshaped, whereas this 

 is not the case with the few males I have seen. In many cases, especiallj' where 

 there is no lorica, the body of the male is almost a true repetition of that of the 

 female, the body being only much smaller, commonly only one third of that of the 

 female. This is the case with the males of Hydatina, Rliinops, Notops brachionus, 

 partly also with those of Synchcvta, and some of the Notoniinatidce f. i. Diglena. Here 

 it is interesting to see how the shape of the males is in accordance with the shape 

 of the female; the thinner the female is, the thinner too is the male. This is also 

 the case with the Asplanchnas where the male of the broad ballshaped A. Brightiuelli 

 and A. Sieboldi is also ballshaped, whereas the male of A. priodonta is oblong. 



On the contrary especially in the plancton Rotifers where the size of the male 

 is very much reduced, there is not the slightest resemblance between the shape of the 

 two sexes. To these, the most reduced of the Rotifer males, we shall return later on. 



As well known the skin of the female Rotifers consists of an extremely 

 thin protoplasmatic laj^er, a syncytium without cell limits and with relatively few 

 nuclei. It is covered with an often very thin cuticula which, when thicker, is termed 

 a lorica. In the males the protoplasmatic layer is commonly still thinner, and the 

 cuticula so thin and hyaline that the males f. i. those of the Asplanchna-species 

 resemble crystalline bubbles. On the other hand some of the males are very opaque 

 so that it is almost impossible to see the interior organs. This is the case with the 

 males of Salpina, of Metopidia, the Gastropiis species and others. Most probably this 

 is due to a thick hypodermic layer; the males in this regard resembling the newiy 



