12 Mr Hickson, On the fragmentation [Nov. 14, 



liberated by absorption of the walls of the brood chambers, and 

 each becomes the centre of a new disc, which is built up by 

 additions of successive rings of chamberlets at the margin. 



The reproduction of Orbitolites therefore takes place by spore 

 formation. 



The spore contains a single nucleus, lying in its 'primordial 

 chamber.' After several rings of chamberlets have been added, a 

 stage is reached at which the nucleus appears to be represented 

 by numbers of irregular, darkly staining masses scattered through 

 the protoplasm of the central part of the disc. 



In the later stages numbers of oval nuclei are found in the 

 protoplasm, often arranged in pairs, and in favourable preparations 

 they may be seen to be undergoing amitotic division. 



(2) The fragmentation of the oosperm nucleus in certain ova. 

 By S. J. Hickson, M.A., Downing College. 



In a former paper* I have described the early stages in the 

 development of the Hydrocoralline Allopora. The following sen- 

 tences in that paper indicate the points that I have thought 

 necessary to investigate with especial care in the development of 

 Distichopora. 



' I can find no trace whatsoever of any division of the proto- 

 plasm in the neighbourhood of the (oosperm) nucleus and no 

 evidence that would lead me to suppose that I have missed any 

 stages of regular segmentation either of the nucleus or the egg 

 protoplasm. 



The evidence, so far as it goes, seems to show that the oosperm 

 nucleus after losing its membrana limitans simply breaks up into 

 fragments and that from these fragments a number of embryonic 

 nuclei are formed that wander into the blastodermic area where 

 they rapidly multiply by a process of growth and simple division. 

 The larger irregular lumps of nuclear substance found only in the 

 earliest stages I take to be portions of the oosperm nucleus that 

 have not so fragmented." 



In Allopora the ova are scattered about in the coenenchym 

 and are not as a rule visible from the surface. In order to obtain 

 therefore a complete series of stages an enormous number of 

 sections must be made haphazard through the colony and in 

 many cases an immense amount of time and trouble is rewarded 

 with perfectly barren results. 



In Distichopora fortunately the element of chance is com- 

 paratively speaking very small, for lai-ge clusters of ova in all 

 stages of development can be seen from the surface even before 

 the coenosteum is dissolved. One can proceed in this case to cut 



* Q. J. Micr. Soc. xxix. 



