9 o 



EDWARD DRANE CRABB. 



haploid number of chromosomes which should be considered. 

 Several investigators have shown conclusively that in many plants 

 and animals the chromosomes form individual vesicles which in 

 turn fuse to form the pronucleus or nucleus as the case may be. 

 Richards ('17) has worked out the history of the chromosomal 

 vesicles in Fundulns, and Nekrassoff ('04) has traced the meta- 

 morphosis of a single chromosome of the second maturation 

 division from the anaphase through several stages to the forma- 

 tion of a large spherical vesicle, such as occurs in L. ..?. apprcssa, 

 in Cymbulia. From this work it appears that the number of 

 chromosome vesicles in the egg pronucleus is the same as the 

 number of chromosomes. However, he does not attempt to cor- 

 relate chromosome number with chromosome vesicle number in 

 this or his later article ('09). More than ten karyomeres have not 

 been found in mature eggs of L. .y. apprcssa. However, various 

 numbers from one, in which all the karyomeres are fused to form 

 the definitive egg pronucleus (Fig. 41) to nine or ten (Figs. 29, 

 37), have been found. It is significant that the maximum num- 

 ber of these vesicles is the same, ten, as the number of chromo- 

 somes in the mature egg and in the first polocyte. 



Other investigators have found that the maximum number of 

 karyomeres in the mature egg is the same as the haploid chromo- 

 some number. Nachtsheim ('19) found this to be the case in 

 Dinophilus ; F. Schrader ('23) in Tctranichus, and S. H. Schrader 

 ('24), in Acrdchismus. No signs of karyomeres were found in 

 male cells of L. ^. apprcssa other than as shown in the pronuclei. 

 In this connection it is interesting that the male pronuclei formed 

 in the sperm receptacle are only of the type having a definite mem- 

 brane (Fig. 44) and resembling those of fowl spermatozoa de- 

 veloped in culture media by Loeb and Bancroft ('12). 



B. In Sperm Cells. 



It appears that the haploid number of chromosomes in the sperm 

 cells is about ten (Fig. 65). The writer hopes to be able to throw 

 further light upon the chromosomes in spermatocytes, primary 

 oocytes and cleavage nuclei in a later paper. 



The principal points in the chain of evidence which indicates 

 that the haploid chromosome number in L. .y. appressa is ten are : 



