STUDIES OF "REPRODUOTIVE ELEMENTS: IL 3JJ 



B. GEN^ERAL CONSIDERATIONS. . 



a. Division. 



Cienknirshj, in liis second pnper on Noctiluca (8, p. 55), speaks 

 of its reprodncfion by means of division and says : — '' Sie wnrde am 

 voMständig'sten von BrifiJifirdI \evfo\(j!;t, dessen Beobachtiini^eii ieli so 

 wolil an norniîil u'eb-mten wie auch an einofekno-eJten Individuen; 

 besfätigen konnte." C^icnkoirskij thus believes with Bri(j]\twcll (5, p. 10) 

 that the division can take place not only in n<n"nial individuals but 

 also in animals in which the tentacle, mouth, etc. h:ive become lost. 

 So fîir as I have observed. I can only confirm Jiohin.s observations 

 (6, p. 1064) that the division takes place only in individiinis in which 

 the tentacles have dis-ippeared. The plane of division is longitudinal 

 to the body of the animal, as Hohin nlso states ; but the first 

 spindle lies in the direction of the longitudinal ])lane, cutting the 

 animal, therefore, transverseh'. The resulting nuclei separate from 

 each other ;ind tiually come to lie opposite, as is ;ilso ])ointed out by 

 Rohin. In the dividing individual, the plane of division of the nucleus 

 apj^ears to lie in the longitudinal axis of the body from the hrst. 



The primary dividing furmw makes its aj)pearance along the 

 dorsal median line of the continuation of the mouth and the Stdbnrgan, 

 and extends till the body hîis taken the form of a biscuit; but the coîu- 

 plete sepnration of tlie body into two parts pn^ceeds, according to my 

 observations, from the periphery towards the central protoplasmic 

 mass, which for a long time remains conti mious, as may be seen in 

 Figs. 10, 11, and 12. Hohin., wlio studied very thoroughly the divi- 

 sion of Noctiluca,, has arrived, so I learn from Buti^clili (6, p. 1068- 

 1067), at conclusions which in the main are in accordatice with nu'ne; 

 the only difference beinii' in the manner of the final division of the 



