134 BULLETIN OF THE 



ence can therefore hardly be explained as due to their failure to pass off 

 with the first lot of eggs laid ; nor can they be eggs which properly belong 

 to the first set of spawn, as their size in comparison with that of the 

 mature eggs (1.1 mm.) sufficiently pi'oves. Therefore I believe that, as 

 Ransom has inferred, these fishes deposit eggs more than once during 

 the season. 



The ovaries are most available for study after the first set of eggs are 

 deposited. As in the case of Fundulus heteroclitus, all stages of growth 

 are shown in ovaries taken during a period extending from one or two 

 months before till a short time after spawning, — the months of March 

 and April. 



In eggs 0.15 mm. (Plate I. Fig. 14) or more in diameter there are 

 two membranes, — an outer more highly refractive, and an inner stri- 

 ated one. In many sections the two are artificially separated (Fig. 15 a ). 

 In ripe eggs the outer membrane had either entirely disappeared, or its 

 structure had become so much like that of the true zona that the two 

 could not be distinguished from each other. Their total thickness is 

 from 15 to 18 /a. In many sections of ripe eggs an outer layer, much 

 thicker than the outer layer seen in the earlier stages of development, 

 was in places separated from the rest of the zona. If it represents the 

 outer membrane of the earlier stage, then the latter must undergo a 

 great change in its later development, for it is now much thickei", and 

 is traversed by the same pore-canals as the deeper portion. 



The rivet-shaped processes which are found in the region of the 

 micropyle are inserted, as Kolliker says, in the thin membrane which 

 lies outside the zona, and which is formed before the latter makes its 

 appearance. They take a much deeper stain than the thin membrane, 

 but I have seen nothing which would warrant one in claiming that 

 they contain each a nucleus. The smallest egg in which these processes 

 could be seen had a diameter of about 0.14 mm. ; only a single thin, 

 structureless membrane was to be made out in this stage. The largest 

 eggs examined had a diameter of about 1 mm. 



When the processes make their appearance, the granulosa is so thin 

 that it is difficult to determine from surface views whether they lie 

 above or below it ; but radial sections show that they lie below. There 

 is no such constant relation between the processes and individual cells 

 of the granulosa as to suggest the origin of the former from the latter ; 

 but at a later stage the heads of the rivets occupy nearly the same 

 plane as the nuclei of the granulosa cells (Fig. 16), and therefore appear 

 to have an intimate connection with the granulosa cells. When the 



