EGG- LAYING HAI51TS OF AMPHITRITE OKNATA VERRILL. 337 



immature ones and from the ccelomic corpuscles by decanting 

 after stirring the mixture in sea-water ; the largest ova and the 

 ripe eggs, those with the first maturation spindle in metaphase, 

 always settle more quickly to the bottom of the dish. The im- 

 mature eggs then settle, and last of all the ccelomic corpuscles. 

 // is not an assumption, therefore, to say that the largest ova includ- 

 ing those in the early stages of maturation, arc more <]itickly influ- 

 enced by gravity than the other bodies floating in the ca'loinic fluid. 

 This is the important fact, and is no doubt due to the larger 

 amount of yolk in such eggs. 1 



If, as Gerould supposes, a hydrotropic attraction is necessary 

 to separate these eggs from the other bodies in the ccelomic 

 fluid, then this influence would be useless for the purpose of 

 separation when the contents of the body cavity are emptied in 

 sea- water. For, surrounded by water, the hydrotropic influence 

 would act in all directions and result in equilibrium. Such is 

 not the case. Indeed, Gerould noticed such facts and in ap- 

 pendix B describes how large individuals should be opened in 

 sea-water. " When the female with an abundance of eggs is 

 found, the maturer ovocytes should be allowed to settle to the 

 bottom, whereas the smaller ovocytes and coelomic corpuscles 

 should be decanted after a few seconds, and before they have 

 had time to sink." 



That gravity forms the differential by which the separation 

 takes place is supported by a considerable number of facts. In 

 the course of one period of oviposition, usually extending from 

 one to one and one half hours, the eggs at first deposited are 

 practically all in the metaphase of the first polar spindle ; in the 

 latter part of the period there is always a considerable number, 

 and sometimes a majority, of ova deposited with the germinal 

 vesicle intact. Upon killing a worm that is through egg-laying, 

 one may still find a few scattered eggs in early maturation. If 

 the separation depended upon a tropism, one does not see why 

 it should be so much more complete at one time than another. 



1 Whether this tendency of large ova to settle quickly is due to a greater specific 

 gravity, or to a greater mass in proportion to the amount of surface offering resistance, 

 the end icsult is the same. This question must be decided by further investigation. 

 In this paper we shall speak of the large ova as though they had a greater specific 

 gravity than the smaller ctclomic bodies. 



