80 BULLETIN OF THE 



been coarser than is usual. If his attention was mainly directed to the 

 outer layer, and if, as I imagine, this is a villous layer, the reason of his 

 statement would be obvious. Besides, he mentions that the canals are 

 not cylindrical, but funnel-shaped, the wider end outermost ; this, too, 

 though suggestive of the capsular membrane, would be entirely com- 

 patible with the idea that he had under view club-shaped villi. And 

 finally, the argument to show that the inner layer is produced after the 

 formation of the outer is exactly applicable in the case of the villous 

 layer, as the observations of Kblliker and my own conclusively show. 



Ransom's ('67) account of the " yelk-sac" (zona radiata) in Gas- 

 terosteus is principally interesting to me from his asserting that the 

 pore-canals as well as the villi increase in number during the growth of 

 the egg, and from his consequent conclusions as to the method in which 

 membranes are formed. The "yelk-sac," he says, is formed in very 

 young ova (200"? or 125 /a, in diameter), in which it is easily recognized 

 by the button-shaped villi attached to the outer surface surrounding the 

 micropyle. The finely dotted structure is first discoverable in eggs y^ /; 

 (180 jx) in diameter, and it is the same in character in these as in the 

 ripest eggs. The membrane is composed of very fine concentrically 

 arranged laminae, each of which is marked by dots of equal size, so 

 arranged as to mark (in surface view) the angles of equal -sized lozenge- 

 shaped spaces, and corresponding in position in the successive laminae so 

 as to form vertically placed lines or striae. In eggs .01 inch in diam- 

 eter there were about 24,000 dots to the [linear] inch, and when the 

 egg had attained .06 inch there were 11,000 to the inch; the distance 

 between dots being scarcely more than doubled, while the diameter of 

 the egg had been multiplied about six times. From this the author 

 argues that there must have been an increase in the number of the dots 

 during the growth of the sac, and therefore that the membrane does 

 not increase by apposition of layers either from the inside or outside, 

 either by the hardening of an exudation or by the conversion of the 

 substance of the yolk into that of the yolk-sac. " It grows in some 

 way by interstitial molecular deposit." A similar increase in the num- 

 ber of the button-shaped villi was also observed to occur during the 

 development of the ova. 



I do not recall that any one has corroborated or disproved these ob- 

 servations, or the deductions made from them ; but I have shown that 

 in the case of Lepidosteus there does not seem to be sufficient evidence 

 to prove that there is any increase in the number of the villi. I believe 

 that a careful investigation of the question in the case of the pore-canals 



