M. UsJSOw'ij Zuuluyicu-Einbryuloyical Iiiccstitjtitiuas. 103 



largecl cells cjf tlic yranulosa and the ovicell, which has been 

 pushed by tlie folds to the superior [jole of the originally round 

 Ciraatiau follicle, are abundantly provided with nourislunent. 

 At this time — that is to sa}', in the period of the '' foldings" 

 Kolliker) — the cells of the epithelial membrane begin to secrete 

 the fluid, fatty, transparent nutritive vittlhis. Consequently 

 the fold-formation of the f/ranulosa only serves for the tempo- 

 rary enlargement of the inner surface of the Graafian follicle, 

 which secretes the nutritive vitellus. In this state each 

 Graafian follicle may be regarded as an inde])endent gland. 

 Ot the vitelline membrane [chorion*) there is at this time not 

 the slightest trace ; so that the description of the nature of the 

 so-called "folding-process" as given by other observers! 

 proves to be very superficial and erroneous (of which I have 

 fully convinced myself). The chorion is formed subsequently, 

 after the nutritive vitellus is completely secreted and the 

 ovum has attained the limit of its perfect development. The 

 chorion, which is at lirst fluid and viscous, is, indeed, nothing 

 but a secreted product of tXio. granulosa of the GraaHan follicle, 

 which may be proved by the fact, among others, that at the 

 commencement of its formation, especially at the superior 

 somewhat acuminated pole, its composition of several thin 

 superimposed layers may be distinctly observed. At the same 

 time there is formed at the above-mentioned thickened part of 

 the chorion, in a manner which, I must confess, is still 

 obscure to me J, its tubular micropyle, more or less widened 

 and funnel-shaped in its upper part. This I have found in all 

 the above-mentioned species and groups of the Cephalopoda. 

 At a very early stage of develojjment the Graafian fol- 

 licle gradually changes its spherical form, and acquires the 

 shape of an egg pointed at the u[)per free pole. The enclosed 

 ovum follows in its form that of the Graafian follicle. The 

 primitive ovicell with the nucleus ( = germinal vesicle) moves, 

 as already stated, to the upper pole of the Graafian follicle, 

 which is now pretty acute {Lolif/o, Sepiola, Anjonauta), and 

 the granulosa of which has scarcely any folds and appears 

 quite smooth at this part. Here, therefore, is the finely gra- 

 nular protoplasm of the primitive ovicell ; and by this means 



* Kolliker (/. c. p. 15) and other observers (Klassen und Ordn. Bd. ii. 

 p. 140-5) quite erroneously take the external pluristratified capsule of the 

 Cephalopod ovum for the chorion, and the true chorion (formeci within the 

 Graatin follicle and always furnished with a micropyle) for the vitelline 

 membrane. 



t Kolliker, /. c. pp. 2-13 ; Brandt, Mediz. Zool. Bd. ii. p. 300, Taf. xx.vii. 

 fig. 27 ; Owen, Memoir on the Pearly Nautilus, p. 42. 



X Where the micropyle is situated there are no folds (" free space," 

 Kolliker), and the mcmbrana granulosa there forms a thin layer. 



