of Mollusks in Holothurise. 31 



a most fortunate circumstance that one of the most celebrated 

 physiologists of the day was working for a considerable time, 

 with a few of his pupils, in Trieste, so that I w^as enabled to de- 

 monstrate the most important of the phsenomena in question to 

 him. I have opened the SynaptcB in the presence of Prof. Wagner, 

 and he could see for himself that the molluskigerous sac was 

 connected with the intestine, or rather with its vessel. I could 

 further show him this sac in two conditions : first, while still 

 containing the ovarium ; secondly, when the contents were the 

 vesicles with living mollusks, in which the motion of the otolithes 

 was very beautifully visible. I was also fortunate enough to be 

 able to demonstrate to M. Wagner the sperm capsules with their 

 moving spermatozoa. My son has likewise observed all the more 

 important facts. 



The development of the mollusks from the yelk closely re- 

 sembles that of other mollusks, e. g. Action (according to Vogt's 

 observations). As in this, there is no vitellary membrane, and 

 two kinds of spheroidal masses are formed by the process of yelk- 

 division, viz. large opake masses, with many yelk- granules, and 

 smaller more transparent spheroids, which also contain stearine- 

 granules, and finely granular molecular masses, but in smaller 

 quantity ; in addition these have their small clear nucleus. In 

 some respects, however, the process of division is peculiar. Be- 

 fore the division of the yelk into two masses takes place, and in 

 yelks which are still quite round, that of the germinal vesicle or 

 clear nucleus occurs. In such round fecundated yelks we 

 find, instead of the germinal vesicle, two somewhat smaller, but 

 otherwise quite similar bodies. Besides, the germinal vesicle 

 does not disappear at all, but in the course of yelk- division is 

 used up to form the clear bodies in the interior of the division- 

 masses. It is perfectly similar in the ovarian ovum and in the 

 fecundated ovum. In the vesicles containing yelks, we find both 

 such as are perfectly spherical and such as begin to show a divi- 

 sion j this commencing division I regard as the indication that 

 the fecundation of all the yelks which are contained in the 

 vesicle has taken place, but yet all still contain the germinal 

 vesicle, and it is either of the same size as in the ovarian ovum 

 and possesses the same viscidity, or there are two smaller ones 

 which must have proceeded from its division. When yelk-divi- 

 sion sets in, first two and then four large yelk-spheroids are 

 formed, each of which has its clear, central nucleus. When the 

 four large spheroids exist, four small transparent spheroids are 

 seen at the intersection of the lines of division upon one side ; 

 these soon become divided into eight, sixteen and more, the four 

 large opake spheroids remaining unchanged. 



In the small transparent yelk-spheroids, the stearine- granules 



