OF THE ROTATORIA. 443 



that subsists between them during this process. We have not space to follow 

 out this piece of comparative physiology in the words of the author, but can 

 only state his conclusions : viz. that the elements which are contained in and 

 solely occupy the ovisac of the Melicerta, are those which, in the ovaries of 

 the higher Mammalia, are restricted to the interiors of the Graafian vesicles ; 

 that, whilst in the former the protoplasmic stock forms one undivided mass 

 from which portions are successively pinched off to fonn the ova, in the latter 

 (the Mammalia) it is divided into small portions, each being contained mthin 

 a special receptacle or Graafian vesicle, the interspaces being occupied by the 

 stroma or tissue of the ovarj-. 



It is in the yelk-matter, derived from the protoplasm, that the red tint 

 noticed by Ehrenberg and others occurs ; the colour depends on red element- 

 ary^ granules, and on highly refractive oil-hke particles. Mr. Gosse suggests 

 that " possibly the colouring matter of these reservoirs may be resolved into 

 the red pigment of the eyes, and the yellow of the jaw-cushion and other 

 parts ; " such a destiny we deem scarcely probable. Moreover the ajDpear- 

 ance of oil-molecules often refracting a red colour, about parts in which active 

 development is proceeding, is a fact very generally observed. A red hue of 

 the ova is seen in PhUodina roseola, Bnicliioyius ruhens, Mastigocerca carinata 

 and Polyartlira ; in Notommata Sieholdii, Asplancha, Anurcea curvicornis, 

 Synchceta jpectinata, and in Lacinularia socicdis. Leydig believes that in 

 many forms, e. g. Brachionus, Noteus, and Euchlanis, one portion of the ovary 

 produces almost exclusively the yelk, and has in consequence a darker colour 

 than the other part, which developes the germinal spaces. This phenomenon 

 has, he remarks, its analogue in various Crustaceans — the Hexapoda and 

 Asellina. It may be here stated, however, that the darker portion of the 

 ovary has assigned to it, by other naturalists, the office of preparing the 

 winter ova, presently described, rather than the yelk, as supposed by Leydig. 

 The preceding account, indeed, applies particularly to the production of the 

 ordinary ova ; the early history of the winter ova referred to will be given in 

 the account of development. 



The Ova. — The Eotatoria develope two varieties of eggs, caUed re- 

 spectively " summer " and '' winter " ova, besides male eggs. Much difference 

 obtains between them, especially in their developments, contents, and later 

 history. The summer eggs have thin, smooth, firm, and elastic shells, so 

 transparent that the course of the changes proceeding within may be watched 

 throughout. In figure they are ellipsoid, oval, or ovoid (XXXVII. 5, 6, 8, 9). 

 They are laid by the animals during the whole coui^se of the summer, and are 

 forthwith hatched. The winter ova, on the contrary, are chiefly produced in 

 the autumn, and are destined to remain in an inactive or torpid state during 

 the winter. They are generally of larger dimensions, often irregular in form, 

 from inequality of the two sides, or from prominences or dej^ressions of the 

 slufaces (XXXIX. 20), and opaque on account of their dark granular con- 

 tents and of their double shell (XXXYII. 21, 22, 24). Caustic potash 

 renders the sheUs clearer and more transparent, and causes some of the 

 iillqualities of their surface to decrease. Huxley says that the tough elastic 

 membrane or sheU is soluble in both hot nitric acid and caustic potassa. 

 Between the two shells is an interspace, more roomy, at the opposite ends of 

 the egg. The inner sheU is thin and delicate, and immediately envelopes 

 the yelk enclosed in its vitelline membrane. The external one is thicker, 

 firmer, and usually of a brownish-yellow colour. Its surface is mostly 

 roughened, or tuberculated, striated, or thrown into ridges, areolated, cellular, 

 or divided into facets, beset with longer or shorter hairs and bristles, and occa- 

 sionally with spines. Examples of such modifications of the surface occur in 



