30 Prof. Miiller on the Development 



the ovary, but the number of those which present an albuminous 

 area has very much increased, and the area is proportionally larger. 

 This stage has been observed seven times. 



2. In each vesicle are fifteen to thirty separate yelks of yyth of 

 a line in diameter, each containing a germinal vesicle. In this 

 state the yelks always appear of an orange colour as in the ovary. 

 Either no traces remain of the diffused yelk-mass, or at times 

 some of its granules and granule-aggregations are left unap- 

 propriated. This stage was observed five times. 



3. In every vesicle there are fifteen to thirty separate yelks, 

 which have begun to divide, e. g. all the yelks consist of four 

 globular masses. This stage was observed eleven times. 



4. All the yelks of a vesicle have developed a ciliated cortical 

 or embryonic layer. Observed six times. 



5. In every vesicle, fifteen to thirty embryos of mollusks with 

 shells are contained. Observed seventeen times. In such a brood 

 as this, some 2400 mollusks come into the world. They all possess 

 a calcareous shell about y^th of a line in diameter, more or less, 

 which effervesces with acids ; they have an operculum upon the 

 foot, and a respiratory cavity similar to that of the Pectinibran- 

 chiata, which are well known to be all unisexual. 



For a long time I did not know how the mollusks made their 

 way out of the Synapta, because I could procure no head portion 

 with the outer end of the sac ; for when the Synapta breaks up, 

 the sac commonly remains in that part which separates from the 

 head. Once, however, I had the good fortune to find a piece 

 with the head in which not merely two molluskigerous sacs (one 

 containing developed mollusks), and a third in a rudimentary state, 

 were present, but where also the two larger sacs had suffered no 

 injury at either their point of connexion with the intestinal 

 vesicle, or at that where they opened externally. 



The third sac was easily distinguishable by its structure from 

 the vesicula Poliana, the walls of which contain the same 

 elongated calcareous discs as the integument of the tentacles. In 

 this still very small sac, the ovarian capsule with its bent end 

 was readily distinguishable ; its external end was firmly connected 

 with the place of opening of the two other sacs, but the other end 

 was free. 



The facts of which I have now given an accurate, though a 

 very general account, differ so widely from the ordinary course 

 of things, that I should myself place no credence in them, had 

 they not almost daily been forced upon my notice. The first 

 complete account of them is now before the Academy, for until 

 the present time I have only communicated them orally in Trieste 

 to a few naturalists, to M. Heckel of Vienna, to Prof. Boeck of 

 Christiana, and to Prof. R. Wagner of Gottingen. I consider it 



