316 C. ISHIKAWA. 



the division commences in this homogeneous part. The median 

 granular part of the spindle of the Si)irochona nucleus, as is given 

 in Hertwiijs Fig. 17, l> and c, is not to he seen in tlie Noctiluca 

 spindle. It is, however, very probable that here the unifurm length 

 of the chromosomes causes the appearance of a distinct median por- 

 tion. One great ditference to be observed between the tw^o, is that in 

 Spirochona and Leptodiscus the archo|)lasm is so rlosely united 

 with the nucleus that it appears as if it formed a part of it. Whether 

 we have to consider the tw^o nuclear parts as a single nucleus, or 

 whether the granular part alone is to be taken as a nucleus is not 

 quite clear, since no membrane is to be seen around the nucleus, al- 

 thoutJfh Hertivui believes in the existence of (^ne from anaK^üv with 

 luiclei of other Protozoons. In J^ e p t o d i s c u s , however. Heriwifj 

 speaks of the existence of a distinct membrane around the t^\() 

 portions of the nucleus taken together. In this connection ticii- 

 wuf says (24/ p. /^l 1-812) : — "Der Kern des Lei)todiscus stimmt 

 S(;mit vollkommen mit dem der Spirochona gemmipara iiberein. 

 Wie ich in einer früheren Arbeit gezeigt, habe, besteht der Nucleus 

 dieses Infusors ebenfalls aus einer feinkörnigen und einer homogenen 

 Substanz, die sich beide gegen einander mit einer glatten Contour 

 absetzen und ç^emeinsam von einer zarten Kernmembran umhüllt 

 werden." Although division of the Leptodiscus nucleus was 

 not observed by Hertwig, the perfect similarity of its structure with 

 that of Spirochona, makes it very [)robable that here also the 

 homogeneous portion plays an active ])art in the cell-division and cor- 

 responds with the archoplasm of the Noctiluca nucleus. 



The occurrence of the kinetic centres — the archoplasms — apart 

 from the nucleus in Noctiluca, deserves special attention. Hichdnl 

 Hertwig (25, p. 10(5) in his very interesting lecture on fertilization 

 and conjugation delivered in lierlin, speaking of the constant occur- 



