102 BULLETIN OF THE 



inquiry to be essentially the same as the perch. The similarity to the 

 perch shown by Acerina vulgaris was recognized by Miiller ('54, p. 189). 

 " In Acerina," he states, ''the egg membrane has the same structure [as 

 in Perca], only it is much thinner, and consequently the tubules are only 

 short, not longer than the breadth of the areas." Eansom ('68, pp. 453, 

 454) also says of this species that its "yelk-sac has an outer layer or 

 ' Eikapsel.' " But he adds, that " the outer layer appears to be contin- 

 uous with, and similar in structure to, the yelk-sac proper." However, 

 Owsjannikow ('85, pp. 17, 18, Taf. I. Fig. 13) has given an account of 

 it which points still more strongly to the resemblance claimed by Miiller. 

 That part of his account is especially significant in which he states that 

 in some preparations the follicle cells have the form of very narrow 

 cylindrical epithelium ; the broad end of the cell is directed outward, 

 the pointed end inward toward the zona. The cells, he adds, lie in a 

 transparent non-staining layer, similar to that in which the spiral canals 

 (in the perch) are located. Finally, a third condition is described in 

 which the cell form is lost. The structure begins with a broad short 

 funnel, and passes at once into a narrow, straight hollow fibre which 

 imbeds itself in the zona radiata. 



The peculiar follicular layer described by Scharff ('88, p. 69, Plate V. 

 Fig. 15) in the interesting egg of the shanny (Blennius pholis) also 

 appears to have begun to undergo a modification in the same direction 

 that leads in the perch to the formation of a capsular membrane. The 

 substance which Scharff calls u interstitial " is, I believe, morphologically 

 the same as the gelatinous secretion of the follicular cells in Perca. 



3. Micropyle and Micropylar Plug. 



Since Doyere ('50) discovered, in 1850, an aperture leading through 

 the membrane of the egg of Syngnathus, and gave to it the name of micro- 

 pyle, there has been a good deal of attention given to that structure. 



Independently of each other, and probably without knowledge of 

 Doyere's discovery, Eansom ('56) in England and Bruch ('55 a ) in Ger- 

 many rediscovered, in 1854, this structure in fish eggs, and both applied 

 the name which had meantime become current through Miiller's ('51 and 

 '54 b ) discovery of a similar canal in the egg membrane of Holothuria, to 

 which he also gave the name of micropyle, borrowed from the usage of 

 botanists. 



Ransom in fact succeeded in observing in the egg of the stickleback 

 the passage of spermatozoa through this opening ; Bruch was less fortu- 

 nate with Salmo fario and S. salar, although he made special effort to 



