120 



s. (^OTO. 



and miitains a sino-le small nudeolu.s. It a])]X'ars in some cases to Le 

 m(~)re weakly stained than the ]>i'()toplasni; hut this is, 1 helieve, owing 

 to the entire ahsenee of any o-j-nnnles IVom the nuclear fluid, \vhi<'h, 

 in conseiiuencc, a])])eai's xvvy clear and trans] KU'ent. ll<^\vevei', 

 the nucleus itself stains e([U'dl_v or often a little more deejrly 

 than the ])i'oto])lasm. As these yolk-cells grow and hecome larger, 1he 

 ])i'oto])i;ism hecomes moi*e and moi'c coarsely grantdai" and stains less, 

 until at last the wliole ]n-oto])lasm is re[)laced hy the yolk-grarniles 

 already desci'ilx'd. In some cases T have ohserve»! cells one half of 

 which omtaincd only yolk-granules, while the otlua- lialf had still 

 a coarsely gramila)* ])roto])lasm (PI. l\ . tig. 7). Lorenz" had 

 ])('rha|)s the young yolk-cclls nhove (lcscril)e(l hcfore him when he men- 

 tions the (V2«au'renc('. directly inside the muscular layer of the hody. of 

 small cells (().00() mm.) ha\iiig a stri^ng ai'iinity I'oi- carmiu. and the 

 centi'al parts of wliicli remain clear and contain each a doi-like l)ody. 

 ( onsidering that the yolk-cells ai-e drained off in consicU'raljIe luuuhers 

 during the ])ei'iod of re))roductive activity, one windd yery natiu'ally 

 ex])ect to meet with tlie ]»henomena of division among the young 

 yolk-cells, and it a]»](ears to me somewhat i'em:u-kal)le tliat I haye never 

 heen ahle to ohser^(' in them aiiv division either diiect or mitotic. 



Yotav-nrcTS — In most genera the ])rimary yolk-diK'ts that ]»i"o- 

 ceed IVom the lohes could not hv observed; hut in Trisloininii I could 

 oiten observe them in sections (1*1. XXI. fig. 7). They have a very 

 small calibre, and are provided with a thin l)ut distinct, membranous 

 \\t\\\. In other species I have often observed yolk-cells passing out 

 from the lobes, but the ducts seemed to close together as soon as the 

 cells had passed along, so that their presence could not 1)e recognised 

 anv longei'. In Trislomiiui again, the secondary and tertiary ducts 

 Avere usirillv liiled with yolk-cells, ;uid could be easily recognised in 



1). Lorenz—/, c p. 5. 



