94 BULLETIN OF THE 



2. Capsular Membrane. 



As I have already pointed out, the capsular membrane, since it was 

 first described by Miiller in the perch under the erroneous supposition 

 that it was the same as the zona radiata of the salmon, has often been 

 confounded with that membrane. In looking over the literature on the 

 egg membranes of fishes, after I had worked out the structure of the 

 villous layer in Lepidosteus, I was forcibly impressed by the resemblance 

 of that layer to the descriptions that had been given of the outer mem- 

 brane in the perch, and at first thought they might be homologous 

 structures. It w r as particularly the account given by Ransom ('68, 

 p. 455, Plate XVI. Figs. 30, 31) of the root-like prolongations of the 

 tubules in the capsular membrane which suggested comparison. It 

 therefore seemed necessary to examine carefully all that had been 

 written on the egg capsule of the perch. The result has not confirmed 

 my first supposition. 



Muller ('54) himself gave an excellent account of the structure of 

 the capsule, and accurately formulated the most interesting question 

 concerning its morphological significance. He described the egg enve- 

 lope (capsular membrane) as about 0.11 mm. thick; its outer surface 

 as covered with six-sided facets, which average 19 /x in diameter. Each 

 facet contained in its centre an open funnel, which was continued into 

 a vertical tubule as long as the thickness of the capsule, and from 2.2 p 

 to 4.7 fi in diameter. In fineness these were comparable to dentinal 

 tubules. They terminated on the inner surface of the capsule in fun- 

 nel-shaped enlargements, just as they did on the outer surface. Upon 

 eggs that had been boiled or hardened in chromic acid, it was possible 

 to see that the tubules had a spiral course, but they also appeared 

 narrower (1.1 //,) than in the fresh state. The tubules were filled with 

 a thickish (albuminous?) mass, w r hich in the fresh egg was clear, without 

 deposits, and under pressure projected from the funnel like a rounded 

 stopper or cylinder, but appeared to be coagulated by boiling and treat- 

 ment with chromic acid. When one compressed the fresh egg to burst- 

 ing, the oily substance of the yolk might be pressed into and through 

 the tubules ; thus w T as effected a delicate injection which might greatly 

 distend them. Between the tubules, however, there was nothing pressed 

 out, which proved that on its deeper surface between the tubules the 

 capsule was closed. In the inter-tubular portions of the membrane, 

 after the eggs are hardened, there were to be recognized, besides a 

 gelatinous nearly invisible material, exceedingly delicate projections or 



