No. I.] SPHYRANURA OSLERL 43 



Stagnation of yolk in the overflow-tube, with the result^that the 

 new yolk-balls forced out are pressed into the uterus and even 

 into the ovarian cavity. The latter, of course, never takes place 

 in ordinary conditions, and we have never seen the former occur 

 except after prolonged pressure. 



We now proceed to give some details as to the minute struct- 

 ure of the female organs. 



As already stated the lobules of the vitellogen are chiefly dis- 

 posed on the lateral, anterior, and posterior faces of the intesti- 

 nal branches; they average about 48 fi in diameter, and are 

 composed of cells and nuclei of 28-32 ^ and 11 ^ respectively. 

 In preparations made with Flemming's fluid the cytoplasma of 

 these is obscured by the yolk-granules, which are' blackened, 

 while the nucleus contains its chromatin in the form of short 

 threads, nucleoli, and granules. In corrosive sublimate prepa- 

 rations, on the other hand, further information is to be obtained 

 as to the cytoplasma, which is disposed in a reticulum, as rep- 

 resented in Fig. 17, from the meshes of which the yolk-granules 

 have been dissolved, probably by the acetic acid employed with 

 the sublimate. 



The Ovary is an oval body, the long axis of which, in fixed 

 preparations, is directed dorso-ventrally, and measures on the 

 average, 100 ^t by 160 ^i. Of the two poles, that which con- 

 tains the ripe and maturing eggs is dorsal, so that the oviduct 

 originates near the dorsal surface, as already explained. In 

 fresh specimens under the cover-glass, the pressure of the latter 

 causes the long axis to be horizontally placed. There is a dis- 

 tinct thickened membrane, formed by the fibrous tissue surround- 

 ing the organ, and in this membrane one can find sometimes a 

 flattened and elongated nucleus, usually less than 2 [.l in thick- 

 ness, which may be regarded as belonging to the fibres forming 

 the membrane. 



In the ovary itself there are cells of two sorts, namely, those 

 which line the internal surface of the membrane, and which 

 therefore may be named the parietal cells, and those which closely 

 fill the cavity, and represent every stage of the ripening ovum. 

 (Fig. 18, a, b, c.) The parietal cells {a) vary considerably in 

 size, averaging in thickness, however, about 6-8 ^ ; their nuclei 

 measure 6 ^ in thickness by 11 ^ in length, and have their 



