Miscellaneous. 437 



detach themselves from the internal surface of the entoderm in the 

 middle of the dorsal region, elongating and attaching themselves to 

 the velum on the one hand, and to the apex of the rudiment of the 

 shell on the other. 



The branchial cavity is a depression of the ectoderm, which is 

 produced between the margin of the shell and tho neck of the larva 

 on the dorsal side behind the anus, which is situated to the right. 

 The mucus-gland is originally a depression of the ectoderm in the 

 middle of the upper surface of the foot. The larvoe brought up in 

 captivity all die at this degree of development : the sequel of their 

 evolution has not yet been observed in a manner complete enough to 

 be the subject of a communication. — Comptes Rendus, September 13, 

 1875, p. 472. 



On the Sexual Reproduction of the J'orfieellitinx. 

 By M. Balbtant. 



Since the time of Spallanzani (1776) it has been generally admitted 

 that the Vorticellians are reproduced by gemmiparity or external 

 budding. Professor Stein, of Prague, has the merit of having shown 

 that this belief only rested on an illusion, and that what was take 

 for a bud separating itself from the parent was in reality the co 

 gation of two individuals of unequal size fusing into a single animal 

 cule. M. Stein sees in this phenomenon a multiplication of the 

 Vorticellians by sexual reproduction, and, as the description which 

 he gives of it differs considerably from the picture which I have 

 traced of this mode of reproduction in the other Infusoria, he uses 

 it as a weapon for attacking my works on this subject. Let us first 

 see how M. Stein describes the facts which he has observed, and take 

 for example his observations concerning a Yorticellian living in a 

 colony, and one of the most widely spread, namely Carchesiwm 

 polypinwm. 



By successive and rapid binary divisions a certain number of indi- 

 viduals of the colony break up into groups composed of four or eight 

 individuals, the size of which is, in consequence, four or eight times 

 as small as that of the ordinary individuals. They remain at first 

 united at the extremity of their common peduncle, and then detach 

 themselves from it successively by the agitation of the cilia which 

 form a crown at their posterior extremity. 



As soon as it is free, each of these little individuals, or mieror/o- 

 nidia (the name given to tbem by M. Stein), whirls rapidly about 

 between the branches of the bush formed by the colony, and at last 

 makes choice of one of the large ordinary individuals, on the side of 

 which it fixes itself by its posterior extremity. The body-walls of 

 the two individuals are absorbed at the point of contact ; and they 

 then communicate freely by their central cavities. During this time 

 the elongated and cylindrical nucleus of each is divided into a num- 

 ber of small rounded fragments, which are dispersed irregularly in 

 the internal parenchyma. Soon after, all the contents of the micro- 



