and Fertilization in the Nernatoidca. 189 



round itself with any second niciubranc. In place of it there is 

 a deposition of a thick layer of a ilocculent, whitisli substance, 

 ap|)cariiin: something like' loose cotton wool. This layer never 

 solidities into a true chorion. Between the eggs there are here 

 and there loose hnnps of this peculiar substance. Small refrac- 

 tive corpuscles are now and then lodged in them. These un- 

 fecundated eggs always remain dark, and never become clear ; 

 nor do they usually acquire such a regular oval form as the 

 fertilized ones. 



This action of the fertilizing corpuscles upon the formation of 

 the chorion presents the more interest, as it reminds us of an 

 exactly similar pluTUomenon in botany. Pringsheim*, as is well 

 known, has discovered that the resting-spores of the Vaucheria 

 lie first of all perfectly naked in the sporangium, and only sur- 

 round themselves with a membrane when the spermatozoids 

 have penetrated through the micropyle into the sporangium. 

 Pringsheim t has made exactly similar observations in (Edoffo- 

 nium. 



We cannot here omit again mentioning the unirapregnated 

 Ascaris mystax which was observed by Bischoff, the eggs of 

 which, according to the statements of this observer, possessed 

 an abnormal, not granular, but lamellar chorion. Nelson had 

 already called attention to a distinction in the structure of the 

 chorion in the eggs of Ascaris mystax, according as they have or 

 have not been fecundated. His statements, however, differ from 

 those of Bischoff. He describes the chorion of his ' false,' that 

 is to say, unfertilized eggs, as granular, w hilst that of the fecun- 

 dated eggs is perfectly smooth. Here we must declare ourselves 

 decidedly in opposition to Nelson. The females of Ascaris 

 mystax that were at our disposal were all impregnated, but in 

 not one of them did the chorion appear smooth, but always 

 exhibited a very distinct structure. With a strong magnifying 

 power, this structure proved to be a delicate division of the sur- 

 face into facets. The facets are of the form of watch-glasses, 

 and slightly concave ; they are visible both on the inner and 

 outer surface of the chorion. They are larger or smaller ac- 

 cording to the individuals. When they are very small, it is not 

 easy to recognize what is before us, and we may then be misled 

 into characterizing the structure as granular, or to suppose that 

 there are very fine canals in the chorion. But whenever indivi- 

 duals are met with in which the facets are 0"004-0'005 millim. 

 in breadth, no further doubt is possible. It must therefore 



• Ueber die Befruehtung der Algcn. Monatsbericht der Berl. Akad., 

 March 1855. 

 t Monatsbericht der Berl. Akad. 1856. 



