THE DEVEFiOPMRNT OF LfOPIDOSIREN PARADOXA. / 



part of the egg there are large granules, measuring, as a rule, 

 between '015 mm. and "02 mm.^ in diameter, and of the 

 characteristic salmon -pink colour, while the interstices 

 between these are filled Avith smaller granules. There is no 

 indication of a region of specially coarse-grained yolk in the 

 centre of the egg, but towards the surface of the '' animal" 

 portion the large granules are absent, and there is present a 

 sn])erficial layer in which the yolk is entirely broken up into 

 very minute particles, whose innumerable reflecting surfaces 

 give to this part of the egg a snowy white appearance when 

 seen by incident light. In the middle of this cap of fine- 

 grained yolk lies the germinal vesicle, the details of whose 

 structure I have not been able to make out satisfactorily. 



As segmentation proceeds, the fine-grained yolk spreads 

 downward towards the ceuti-e of the egg — the smaller 

 blastomeres being distinguished by their fine-grained yolk 

 from the larger lower blastomeres, where the yolk remains in 

 large granules." Even in this latter region, however, the 

 division planes become marked out by a septum of fine- 

 grained yolk. 



As mentioned in my former paper, the segmentation 

 cavity begins to appear Yery early, in the form of chinks 

 between the niicromeres. In an egg of Stage 8^ (PI. 1, fig. 1) 

 the cavity within the egg still remains in the form of such 



1 Altliougli the eggs laid by one female may be said to be on the whole 

 more coarsely grained than those of aiiotlier, yet there is much variation even 

 amongst tlie eggs laid by a single female ; e. g. in four eggs taken from one 

 nest tiie large yolk granules averaged "018, "018, "020, and '022 mm. in 

 diameter respectively ; in three eggs taken from another nest the correspond- 

 ing dimensions were '015, •015, and "02 mm. 



^ This statement must be taken as true only in a general sense ; every now 

 and then one meets with a few coarse granules within the micromeres ; while 

 in the region of the macromeres irregular patches of comparatively fine- 

 grained yolk frequently appear. 



' By " Stage n " I mean an e^g whose external features have reached the 

 stage of development represented by fig. n of my previous paper. At Prof. 

 Lankester's suggestion I have had a figure (Text-fig. 1) prepared to illustrate 

 the chief stages, and so to obviate the necessity of frequent reference to the 

 )>lates of my previous paper. 



