1904.] NATURAL SCIENCES OF PHILADELPHIA. 741 



aperture between the three tail lobes. The atrium is lined with a 

 glandular epithelium, as is also the proximal end of the cloaca; the 

 remainder of the cloaca bears a cuticular lining. 



The egg-cells contained in the lateral diverticula of the ovaries 

 of adult females (individuals whose external cuticula is of a dark color) 

 are all ovocytes of the first order at the end of the growth period (fig. 1, 

 PI. XLIX). The nucleus is more or less central in position, contains 

 one large dcepl}^ staining nucleolus, and a nuclear sap which shows no 

 trace of chromatin and only in a few cases exceedingly delicate linin 

 fibres ; even strong iron hsematoxyline stains fail to demonstrate chro- 

 matin particles. The cell-body evinces a zone of yolk globules (shaded 

 in figs. 1 and 15), placed near the periphery; while the cytoplasm is 

 coarsely alveolar, and the meshes of very regular size in the perinuclear 

 area. 



Wliile these ovocytes are passing from the "ovaries" to the "uteri," 

 but before they have entered the latter, their nuclei are in prophases 

 of the first maturation mitosis; such stages are shown in figs. 2-5. 

 The nucleolus becomes smaller and stains less intensely, while there 

 appear, usually close to it, chromosomes in the form of long loops 

 (figs. 2, 3) ; these do not first appear simultaneously, but successively. 

 These chromosomes shorten into the form of minute dumbbell-shaped 

 bodies, seven in number (fig. 4), and for the first time is seen in the 

 nucleus an achromatic network (fig. 5). These are bivalent chromo- 

 somes, as shown by their shape and by the fact that there are fourteen 

 single chromosomes in the cells of the embryo. Two points are 

 remarkable in regard to them : first, that no trace of them is to be seen 

 in the preceding rest stage; and second, that they appear in succession 

 close to the nucleolus, and later arc frequently found in a compact 

 group — a condition infrequent in a prophase. The evidence is that 

 these chromosomes come out of the nucleolus, and that during the rest 

 stage they are contained within it. Such a condition has recently 

 been demonstrated for the egg of Asterias by Hartmann (1902); but 

 that it is by no means a usual condition in Metazoa, on the contrary is 

 decidedly unusual, was previously shown by me (1898). As the ovo- 

 cyte enters the uterus the seven double chromosomes are arranged in 

 the equator of the first polar spindle (fig. 6; fig. 7, a pole view of the 

 spindle); this has the form of the corresponding spindle of Ascaris, 

 and no centrosomes are demonstrable. As the ovocytes, closely com- 

 pacted together, are propelled rapidly backward along the uteri antl 

 so through the oviducts into the atrium, the spindle moves gradually 

 nearer the periphery of the egg. 



