434 RICHARD EVANS. 



be formed by the separation of the daughter chambers. The 

 other chambers situated further iu illustrate a slightly more 

 advanced stage in the division of a chamber. The space be- 

 tween these latter chambers is not furnished as yet with its 

 lining cells, or at least they have not flattened out to form flat 

 epithelium. The large cell with a granular nucleus, situated 

 close to the nutritive vacuole [n.v.) on the inner side, is about 

 to flatten out to form the lining of the exhalant canal that is 

 being developed between the two chambers. 



From the above facts the following conclusions may be formu- 

 lated : — The cells of the flagellated chambers divide by mitosis. 

 They become too numerous to constitute one chamber, and 

 consequently are separated into two groups or daughter 

 chambers, which have their apopyles facing each other, and 

 at first, at least, open into a common exhalant canal lined by 

 cells with granular nuclei. 



Appendix E. 



On Mitotic Division in the Cells of the Free- 

 swimming Larvae of the Young Sponge. 



Though it was not the object of this paper to describe the 

 mitotic division of the nuclei, still, owing to the fact that in 

 sponges little has been done on this line of inquiry, and that 

 I have from time to time seen phases in cell division and 

 drawn them, it is deemed advisable to record them. Though 

 they are in no way complete, they may serve as the bases of 

 further research. 



The ciiromatin, immediately after the nucleus has lost its 

 ordinary characters, presents the form of small granules — 

 about a dozen in number — which are by no means easily made 

 out (fig. 42, 1 a). 



During the next stage the chromatin granules become 

 arranged in the form of an equatorial plate in which the indi- 

 vidual chromosomes are difl&cult to identify. The threads of 



