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pearaiîce. Above the testis, at the point where the testis tapers into the vas deferens, 

 we very often, in the male sex, find one or two globular bodies, commonly hyaline 

 sacs, filled either with one, two or many opaque cor[)uscles, often with sharp sides. 

 They also occur now and then in the females, but much more rarely, their struc- 

 ture and size differ from specimen to specimen. They have been interpreted in very 

 different ways by Cohn and Weisse as remnants of yolkmasses, deriving from the 

 eggs, by Leydig as "Harnkonkremente" and the globular vesicle as rudiments of the 

 rectum. Whether the last supposition is correct is perhaps doubtful, but as I have 

 seen the lateral canals open into it, in Euchlanis lyra, I am inclined to think that 

 Leydig's interpretation is really correct. 



Chapter V. 

 Remarks Relating to the Reduction of the Male Sex. 



In the foregoing pages many examples have been given relating to the reduc- 

 tion of the male sex in the Rotifera. We have seen that the reduction may be 

 carried so far that, as in Polyarthra, the male is really nothing but a sperm -sac, 

 surrounded by a protoplasma, containing a number of oil globules and coated with 

 a cuticula, anteriorly carrying a tuft of long cilia. If a freeswimming organism is 

 really to play a rôle as a fertilising creature, it is obvious that a greater reduction, 

 cannot take place. The question now is: What has caused this enormous reduction, 

 a reduction so great that in the whole animal kingdom it is only very rarely met 

 with, and most probably is really the most complete we, upon the whole, know. 



As well known, the reduction of the male sex in the animal kingdom is by 

 no means only restricted to the Rotifera. However, where it is not onlj' limited to 

 reduction with regard to size, it is almost alwaj's combined with parasitism. This 

 is always the case where we have a reduction of such a radical nature that the 

 males are really reduced only to sperm-sacs almost, with the necessary clasping 

 organs for fastening or for locomotion. In many cases the males are parasitic upon 

 or within the females. Strongly reduced males of this kind we find for instance in 

 the Cirripedia, parasitic Isopoda, Copepoda, and in Bonellio. In the Rotifera however 

 we have animals where parasitism of the males is an unknown phenomenon. Males 

 and females live a freeswimming or freely creeping life, swimming side by side in 

 the same water masses; at first sight it is wholly unintelligible what has caused 

 this enormous reduction in the male sex. 



We are here facing a problem which has not hitherto been solved, mainly 

 because it has not been set up. Our hitherto very restricted knowledge of the male 

 sex in the Rotifera is the main cause of this in itself very peculiar phenomenon. 

 In the following pages an attempt is made to solve the question. 



43* 



