137 325 



as stored nutriment, yolkmasses, deriving from the egg. As it has been pointed out 

 with regard to the Asplanchna species tliat the animals grow very considerably and 

 that simultaneously herewith these masses diminish in size, it is most probable 

 that this stored nutriment is really of significance in the short life time of these 

 animals. 



Male organs: The male organs in the Rotifera consist in 1) the testis, 

 2) the vas deferens or ductus seminalis, 3) the so-called prostata glands, 4) the penis. 



The testis is a large, pearshaped or globular organ, lying in the middle of 

 the body and often filling the greater part of the body cavity. Especially in the 

 rudimentary males of the plancton Rotifers, f. i. Polyartlira, Triarlhra, it is extremely 

 large in comparison with the whole body. It is held in place by means of a broad, 

 flattened band which reaches from the forepart of the testis to the wheel-organ, and 

 as mentioned before commonly regarded as a rudiment of the alimentary canal. In 

 some species, e. g. Hijclatina, it is further fastened to the dorsal side bj' means of a 

 special tissue, fastened to from three to five of the transversal muscle bands. 



The development of the spermatozoa has been studied bj' Whitney (1917, 

 p. 305 and 1918, p. 325), he states that the number in all the species investigated 

 is remarkably small; the highest number of mature spermatozoa found in the testis 

 being about 300 (Asplanchna). Earlier authors have often pointed out that the testis 

 of the Rotifera contains two sorts of spermatozoa ; the one sort has a well-developed 

 head, and long undulating tail; these spermatozoa are very motile; the other sort 

 are short, stiffened staffs, without head and immotile; the last named, almost al- 

 ways lie pressed together near the opening of the testis, almost parallel with each 

 other; they were formerly (Cohn) interpreted as a peculiar muscular structure of 

 the testis; they are always much smaller in number than the motile ones. In two 

 consecutive papers Whitney (1917, p. 305 and 1918, p. 325) has shown that the 

 number of motile spermatozoa is exactly twice the number of immotile sperma- 

 tozoa produced. Both sorts of spermatozoa possess heads, but the immotile sperma- 

 tozoa are regarded as rudimentary and functionless. The functional spermatozoa, 

 having fertilised a parthenogenetic male egg, always gives rise to a female indi- 

 vidual. If the male egg had not been fertilised, a male would have been produced. 

 Now as it ha^ been ascertained, that in every male a certain percentage of the 

 sperm-cells degenerate, and a certain percentage develop noi-mallj% thus giving a 

 definite ratio of degenerate and normal sperm-cells, and as all fertilised eggs develop 

 into female young, it seems safe to conclude that the degenerate sperm-cells are 

 the male-determining ones, and that the normal sperm-cells are the female-determ- 

 ining ones (Whitney 1918, p. 333). It has often been supposed that the function of 

 the staff-like rudimentarj' spermatozoa is to perforate the skin of the female during 

 the pairing process. 



The vas deferens, its length and its structure, is dependent upon the occurrence 

 of a true penis. 



In the most primitive forms the male sexual opening lies dorsally on the foot; 



D. K. D. Vidensk. Selsk. Skr., naturv. og matheni. Afd., 8. Bække, IV, 3. 43 



