OOGENESIS AND EARLY EMBRYOLOGY ASCARIS 535 



the dyad form in the haploid condition, although the method of 

 their formation was entirely unknown to him. 



III. MATERIAL AND METHODS 



The material was all obtained from freshly killed dogs, care 

 being taken that only specimens of Ascaris canis Werner were 

 employed. The worms were immediately removed from the in- 

 testine of the host, placed in normal salt solution, and kept at 

 body temperature until they could be killed. The posterior end of 

 the worm w-as clipped off and the ovaries were at once stripped 

 out on to a glass plate and fixed, the whole process taking but a 

 few seconds. Hermann's fluid, Flemming's fluid (strong) , Bouin's 

 fluid, Petrunkevitch's modification of Gilson's fluid, acetic alco- 

 hol, and Carnoy's fluid were used as fixatives. The most favor- 

 able fluids were those of Carnoy and of Petrunkevitch. 



The best sections wer§ obtained from material imbedded in 

 paraffin by the benzol-chloroform method. These were cut 

 15m or 30^4 in thickness. Heidenhain's iron-haemotoxylin stain 

 followed by a counter-stain of Bordeaux red or Orange G was 

 the staining method usually employed. The Biondi-Heiden- 

 hain triple stain, safranin-licht grlin, and alizarin-krystal violet 

 stains were also used for the study of the linin and the plasmo- 

 some; likewise for the cytoplasmic structures of the maturation 

 stages. Schneider's acid carmine was used in the study of 

 whole mounts and smears, but was valuable only for a rapid 

 ascertainment of the age of the cell or the number of the 

 chromosomes. 



IV. EXPERIMENTAL EVIDENCE 

 A. OOGONIAL DEVELOPMENT 



The youngest oogonia appear as very small cells (fig. 1), 

 closely packed in a single layer around a very fine central core, or 

 rhachis. .The diameter of the nucleus is about one-half that of 

 the cell; its chromatin is centrally located in a single, compact, 

 more or less spherical mass of regular outline, and is of homo- 

 geneous appearance after all the methods employed. The cyto- 



