444 GEIJEEAL HISTORY OF THE INFUSORIA. 



Anwcea Testudo, A. serridata, Notommata Sieboldii, N, Myrmtleo, Melicerta 

 7'ingens, Ascomorplia Oermanica, Lacinularia socialis, Scaridium longicaudum, 

 Hydatina senta, Anurcea valga, &c. Ehrenberg was not prepared to admit 

 the existence on ova of actual hairy processes, but supposed them to be the 

 hair-like filaments of Hygroerocis, or of other Algae. This supposition may 

 in some cases be correct ; for ova, like other bodies in the water, may become 

 the nidus for the growth of various microscopic plants and animals. That 

 some ova, however, are actually hairy is evidenced by their visible occuiTence 

 in that state even whilst still within the abdomen of the parent ; as may be 

 seen in the ova of Hydatina senta, of Notommata Parasitiis, &c. Both winter 

 and summer ova may often be met with in the same animal (XXXIX. 16) — 

 the one kind perhaps still in the ovary, the other on the point of expulsion ; 

 or, it may be, both sorts may be carried about attached to the posterior part 

 of the parent animal. This last occurrence is noticed by Leydig in Brachionas 

 Baheri, 



These two varieties of ova were recognized by Ehrenberg, who assigned 

 them the names applied to them. Mr. Huxley suggests, instead of the term 

 < winter ova,' the appellation, ' ephippial ' ova, to indicate their analogy with 

 the similar eggs of Daphaia and other Entomostraca. 



When recounting the propagation of Notommata Sieboldii, Leydig remarks 

 that male and female ova are not developed together in the same animal. 

 This fact has been extended by Cohn to apply to the whole family of Rota- 

 toria. According to him the ephippial are always distinguishable by their 

 external characters from the common summer ova, particularly by their much 

 smaller dimensions. They have thin, transparent shells, and are chiefly pro- 

 duced at those seasons when ' ephippial ' ova are generated. Their develop- 

 ment follows the same course as that of the ' summer ' ova ; but they are pro- 

 duced in very much smaller numbers, — a circumstance that affords another 

 reason for the paucity of males compared with females, whenever a collection 

 of Rotatoria is examined. 



When the development of summer ova in the ovary has proceeded to the 

 point we have mentioned, and the egg is already become a distinct body from 

 the general substance of the ovary (XXXYIT. 2 d), it is slowly moved down- 

 wards towards the passage or o\iduct (XXXVII. 2/), which ends in the 

 cloaca (XXXYII. 32 d) ; and it is in this part of its course that the shell 

 becomes perfected. In the majority of the Rotatoria the ova are at this stage 

 extruded, the further phases of development proceeding externally to the 

 animal ; in others they are detained in their passage until the embryo is 

 more fuUy elaborated, or even until it is perfect and released from its shell. 



The size of the ova prior to expulsion XXXVII. 32 d; XXXYIII. 26p) 

 is very extraordinary, so much so that a single ovum will sometimes occupy 

 the larger portion of the interior of the animal. The completed egg of Me- 

 licei'ta. has an average length, says Williamson, of y^-yth of an inch, and a 

 diameter of yfo^^- -^^® ^SS^ ^^ some Hydatince are -g-g-g^-'^' ^^ Lacinularia 

 ■j^th of an inch and upwards in diameter. 



In several Rotatoria, two or more ova become agglutinated together n^r 

 the termination of the oviduct, or in the cloaca, and are expelled together en 

 ■masse, and still remain adherent to the parent, close to the cloacal outlet at 

 the base of the tail. This is exempHficd in Triarthra (XXXYIII. 30 d), Po- 

 lyarthra (XXXIII. 400, 401), Anurma (XXXY. 496; XXXIX. 16), and 

 Noteus. 



The oviduct, or passage from the ovary to the cloaca, is a membranous tube 

 formed by a prolongation of the tunic of the ovary. It is always extremely 

 dilatable ; and sometimes an egg is so long detained in its lower part, that it 



