544 A. C. WALTON 



or synaptic stage similar to the one described above for A. canis. 

 This clumped mass breaks up into a tangle of interlacing fibers, 

 each one of which is longitudinally split, and haf5 its contained 

 chromatin unevenly distributed along its length instead of being 

 deposited in definite chromatic bodies. These threads radiate 

 in pairs from the nucleolus as a center, and the chromatin 

 collects into rods on each thread, thus giving pairs of rods; but 

 each rod is itself already longitudinally divided, owing to the 

 double nature of the thread around which it is formed. Each 

 chromatic body, or chromosome, is therefore made up of four 

 parts, closely bound together by linin. A transverse constric- 

 tion appears soon after (taf. 30, fig. 38),— at the time of the dis- 

 appearance of the linin threads, — leaving the chromosomes, now 

 octads in form, lying free in the nucleus. During this period, 

 according to Marcus, the nucleus loses its limiting membrane 

 and assumes a remarkable star-shaped appearance, with one of 

 the eleven (reduced number) octads occupying the outer ex- 

 tremity of each ray. The chromosomes are now ready for the 

 maturation divisions. 



By the time that the chromosomes of the prophase in A. canis 

 have become differentiated into definite tetrads, the cells have 

 lost all connection with the rhachis and lie free in the oviduct, 

 not very closely packed, and have a slightly rounded contour. 

 While the cells still show, in longitudinal section, approximately 

 pear-shaped outlines, the nucleus no longer occupies the larger 

 end of the cell, but lies near the middle of the longitudinal axis. 

 The cells now gradually assume a more nearly spherical outline 

 (figs. 20 and 21). 



The thirty-six chromosomes (fig. 20) begin to show a trans- 

 verse constriction, becoming dumb-bell shaped. The plasmo- 

 some, when present, is at a little distance from the nuc'ear mem- 

 brane. The cytoplasm clearly shows a granular reticulum, 

 interspersed with numerous medium-sized vacuoles. 



Soon after the appearance of the transverse constriction 

 {Qiierkerhe of Haecker), a longitudinal split or a constriction 

 (fig. 22), at first very faint, appears in each chromosome. Dif- 

 ferences in the sizes of the chromosomes also appear (fig. 22) ; 



