450 GENERAL HISTOTlY OF THE rjfFUSOKlA. 



that Rotifera found at great altitudes among snow do not attain a complete 

 development, but retain, as he expresses it, an ovate contracted figure ^dthin 

 an egg-like envelope or capsule, through which food reaches them by a 

 funnel-shaped canal. All the functions of life he represents to go on as 

 usual under these peculiar conditions of existence, including the deposition and 

 hatching of eggs. This account reads like a description of an encysting- 

 process in the first degree — that, viz., for self-defence and preseiTation — 

 such as is illustrated in the formation of an open sheath around Stentor, as 

 stated by Cohn (see p. 284). 



Contents and Development of Winter Ova. — The contents of " winter " 

 widely difier from those of '^summer " ova. Mr. Gosse gives the follomng 

 account of those of Melicerta rinc/ens. He writes — " Opening one or two 

 cases (urceoli), I find one and another very curious egg-like bodies, not sym- 

 metrical in shape, being much more gibbous on one side than the opposite, 

 and measuring y^th by gi^th of an inch. Each was encircled by five or 

 six raised ribs running parallel to each other longitudinally, somewhat like 

 the varices of a wentle-trap : viewed perpendicularly to the ribs, the form 

 is symmetrical — a long narrow oval. The whole siu'face between the ribs 

 appeared punctured or granulate, and the colour was a dull-brownish yellow. 

 Under pressure it was ruptured, and discharged an infinitj^ of atoms, of an 

 excessive minuteness, but every one of which for a few seconds displayed 

 spontaneous motion. Their whole appearance, and the manner in which 

 they presently turned to motionless disks, were exactly the same as the 

 spermatozoa which the male eggs of other Rotifera contain, except that 

 these were so minute." 



Mr. Dalrymple describes similar peculiar ova in Notommata (AsjjJancJma) 

 to consist of an aggregation of cells and of pigment-granules, without a dis- 

 tinguishable germinal vesicle. 



The most complete and satisfactory account of the structure and develop- 

 ment of the winter ova is supplied by Prof. Huxley in his Histoiy of Laci- 

 nularia (T. M. S. 1852, vol. i.); we wiU, however, preface it by Leydig's 

 description. AYe learn from this writer that in winter ova, a space filled 

 with fluid usually intervenes between the yelk at each pole or end of the 

 egg, and the inner shell, as in Tubicolaria, and that, according to Weisse's 

 observation of Bracliioniis urceolaris, the outer shell, when the embiyo is 

 ready to come forth, springs open in a valvular or a lid-like manner. The 

 central portion of the yelk has a darker and more granular appearance, and 

 is surrounded by a clearer peripheral or cortical lamina, as in BracMonus 

 Baheri, Notommata Myrmeleo, and N. centrura. Intermingled \\ith the yelk- 

 molecules are numerous clear vesicles, and oftentimes fat-particles ; moreover, 

 the yelk oi Notommata Sieboldii has a yellowish-red coloiu' (XXXVII. 27, 28). 

 These " lasting ova," as Ehrenberg has otherwise named them, are always 

 developed externally to the animal. Like the summer eggs, they are fre- 

 quently carried about by the parent ; it would not seem, however, that they 

 ever accumulate in groups about the cloaca, but that mostly the eg^ is 

 solitary, and that two or three are of rare occurrence. Thus in BracMonus 

 Bakeri and in AscomoriDha never more than one is present, in BracMonus 

 rubens a couple are occasionally noticed, and in Notommata Siebolclii the 

 highest number seen was three. 



Concerning the changes ensuing on development, Leydig states that, " on 

 the formation of a membrane around the commencing ovum in the ovary, 

 the peripheral portion of the yelk exhibits numerous clear spots, which recall 

 the appearance of the small cells originating from repeated fission of the 

 yelk of the summer ova. From tliis we may conclude, either that the germi- 



