172 EDWIN G. CONKLIN 



certain intrinsic conditions, which are for the most part unknown. 

 In some instances there is a direct relation between egg size and 

 bod}^ size, as in the male and female eggs of Dinophilus, phyllox- 

 erans, rotifers and spiders (Montgomery '08). On the other hand 

 there is marked dimegaly of the sexes in each species of Crepidula, 

 as shown in table 1, without any corresponding dimegaly of the 

 sex cells, but it is possible that protandric hermaphroditism may 

 sometimes occur in these species (Conkhn, '98, Orton '09). It 

 is well known that egg fragments produce smaller embryos than 

 entire eggs, and Zur Strassen ('98) has shown that from two fused 

 eggs of Ascaris megalocephala a giant individual may result. 

 According to Morgan ('04) and Chambers ('08) frogs' eggs which 

 are smaller or larger than usual give rise to individuals which 

 are smaller or larger than the mean. All of this shows that within 

 a species there may be a relation between body size and the size 

 of the 'Ausgangszellen.' But at the most this is only one factor 

 of several which determine body size, and in many cases, as in 

 the genus Crepidula, the other factors are the more important 

 ones. 



In the case of different species or varieties, even though closely 

 related, it is evident that egg size in general cannot be directly 

 correlated with body size. Here the rate and duration of .cell 

 growth and cell division are the most important factors in deter- 

 mining body size. 



d. Blastomeres. In the early cleavage of the eggs of these gas- 

 teropods the blastomeres are, cell for cell, the same, except for 

 size, in all the species, whatever the size of the egg may be. The 

 direction of cleavage and its relation to the chief axis of the egg, 

 the rhythm of cleavage and the relative sizes of daughter cells, the 

 constitution of the blastomeres, whether protoplasmic ordeuto- 

 plasmic, and the ultimate destination of the individual blastomeres 

 is the same in all the species of Crepidula, (figs. 4 to 12). In all 

 of them the ectomeres are separated from the entomeres as three 

 quartets of micromeres, which contain most of the cytoplasm of 

 the egg but no yolk (figs. 4 to 7) ; in all of them the mesomere 

 (4c?) arises from the left-posterior macromere, and contains both 

 yolk and cytoplasm; in all species, the entomeres are the four 



