MILK. FORMATION. 109 



these capsules show that the two spaces are always separated by a 

 rather thick wall; certainly much thicker than that which 

 separates the new yolk space from the exterior. This latter wall, 

 in fact, i- usually very thin. It consists, however, of an extremely 

 thin connective tissue layer in addition to the ovarial epithelium, 

 liv < .ireful handling the epithelium can be -tripped <>tY and the 

 thin la\T .-iiclosing the yolk space left intact. 



"Ilit- \ery external position of the yolk -pa. es of \\hich there 

 ina\ ! .-r.il in a single capsule make- it evident that 



in -in- 1. 1 i In cells of the old follicular membrane an- cn-a-ed in 

 tin- ]>n id in lion of yolk in this new and unusual -ite. The 

 |ini<lm lion of this yolk i> necessarily accomplished by the cells 

 which form the external theca a tissue from the former ovarian 

 stroma, \\lii-h in the late growth stages of the cap-ule of large 

 Mies a very thick, firm, essentially connect i\e ti ue 

 la\er i -in lii-ing possibly some scattered derivative- of the m-r- 

 niin.il epithelium -whose cells normally take no part in yolk 

 toriiiaiii.ii. 



|u-t \\liai it. is that transforms these non-yolk-producing cells 

 into ell- ai ti\ely engaged in yolk production, ii \\mild lie nm-i 

 inii n sting to know. While confessing very complete ignorance 

 as to thi- i ause, it seems worth while to note that the cells ichich 

 here hike n(> n new function do so at the time v//r;/ the "normal" 

 tin * - do is to degenerate and be '/. 



In thi- connection it should be stated that the true lollicular 

 e!l- iln-e \\hich ha\'e previously been engaged in pa--iir^ .-n 

 tin- . Dii-tiiueiit> of yolk to the egg are apparently the lea-t 

 liable i.t anv of the capsular cells to take part in any later yolk 

 production. < >nl\ occasionally in a group of cap-ule-, each of 

 \\hich mav In- producing yolk at one or more point- externally, 

 \\ill one tin, | th.it the follicular cells ha\- continued or rather 

 ha\e recommenced to produce yolk. What I ha\>- ob-er\ed 

 \\ould indicate that these follicle cells iu-\er in an\ case become 



acti\e until after \ oik production ha- been initiated ill the more 

 exiernal la\er-; but of this latter point 1 ,1111 inn certain. 



That the \ello\\Uh tluid enclo-ed in the-e \olk -|iac.-- i- true 

 \olk i- indicati'd b\ its microscopic appearance. The question 

 i- |io-iti\,-l\ .uul affirmatively answered by the chemical anal 



