MUSEUM OF COMPARATIVE ZOOLOGY. 69 



which traverse the membrane, would in his opinion sufficiently explain 

 the absorption of the water into the interior of the shell membrane. 

 (Compare also Vogt, '42, pp. 27, 28.) 



From this summary it is evident that Vogt had under consideration 

 appearances which were due to the pore-canals of the zona radiata, and 

 that he moreover believed in the presence of canals, but it cannot be 

 claimed that he demonstrated their existence. Unlike his predecessors, 

 he rightly claims that the shell membrane (in Salmo umbla) originates 

 in the ovary. 



In a paper written in 1845, but not published till many years later, 

 Vogt et Pappenheim ('59, pp. 357, 361, 3G2) also maintain that the 

 shell membrane of the eggs of fishes, w T hich is uniform and elastic, is 

 constituted by the fusion of a cell layer formed in the ovary, and there- 

 fore not to be compared with shell membranes which are produced in 

 the oviduct. They made the mistake of insisting that " this cell layer 

 is not to be confounded with another epithelial layer which one finds in 

 the ovisacs of the youngest ovules, and which is composed of large ex- 

 tremely pale cells which subsequently disappear and give place to this 

 second layer." 



Meckel von Hemsbach ('52, p. 421, Taf. XV. Fig. 1) saw and fig- 

 ured a radial structure of the "zona pellucida " in the case of Cy- 

 prinus auratus, after treating the membrane with acetic acid and 

 crushing it, but he expresses no opinion as to the real nature of the 

 striation. 



Leuckart ('53, pp. 796, 797), who probably had not yet seen Meckel's 

 paper, was evidently not impressed with the explanation which Vogt 

 adopted to explain the appearance of the outer membrane in Coregonus ; 

 for he says simply, " That which characterizes the eggs of teleosts is 

 the possession of a special firm egg-shell (chorion), which is already 

 formed in the follicle around the primitive yolk membrane, and generally 

 presents a delicate marking resulting from regularly grouped granules 

 or points." 



During the five years beginning with 1853 there appeared a large 

 number of papers dealing with the egg membranes of fishes, and the 

 subject was brought to a temporary conclusion by the thorough work 

 of Kijlliker. 



Aubert ('53, pp. 94, 95, Taf. VI. Fig. 1) was the first to figure well 

 the appearances due to the pore-canals of the zona radiata. In addition 

 to " a very finely granular, but otherwise structureless skin, which en- 

 velops the yolk," and which I believe must have been in his opinion the 



