Watson: The Genus Gyrocotyle. 403 



by most methods as deeply as does the nucleus but easily dis- 

 tinguishable from it in strongly decolorized haematoxylin 

 preparations, and also in borax carmine-Lyon 's blue prepara- 

 tions. Plate 41, figure 54 shows the origin of this body as an 

 extruded nucleolus, distinguishable even when within the nuclear 

 membrane from the chromatin nucleolus proper. Probably only 

 one such body, or * ' yolk-nucleolus, " is formed during the 

 development of the ovum. In fully formed ova this yolk- 

 nucleolus has greatly decreased in staining intensity, appearing 

 as a mere shadowy ring with a dark center (pi. 41, fig. 51). 



The ripe ovum passes from the follicle into the oviduct where 

 it takes on an irregular elongated form, strongly suggesting 

 amoeboid movements. This form has also been noted by Lonn- 

 berg (1891, p. 40). These ova are the largest cells in the body, 

 measuring about 26^, by 15/A. Their cytoplasm is very dense, full 

 of shapeless masses of material. The nuclei are about 12/A in 

 diameter, clear, with heavy deeply staining chromatin reticulum 

 and large round nucleus, from 5/x to 6/x in diameter. The nu- 

 cleolus is larger than any other nucleus in the body, except those 

 of the ganglion cells of the first order and possibly the nuclei of 

 yolk cells. The large, clear bright nucleus with its dense deep- 

 staining nucleolus makes the ovum easily recognizable even under 

 low magnification. 



The processes of maturation, which have not been observed, 

 probably occur after the ova reach the receptaculum ovorum. 

 Division of oogonia in the follicles of the ovary appears to take 

 place by true mitotic division. Equatorial plates and anaphases 

 have been observed, but no attempt has been made to work out 

 the phases of mitosis. There are no indications of amitosis, either 

 here or in the follicles of the testes. It seems probable from the 

 evidence in Gyrocotyle, that Child's (1907) amitotic figures are 

 the result of confusing the "yolk-nucleolus" with the nucleus 

 proper. Such figures as are shown in plate 41, figures 52, 53, 54, 

 could easily be taken for unequal mitotic divisions of the nucleus, 

 were it not for the differential staining. 



The vitellaria are follicular, each follicle being surrounded 

 by a fibrous tunica propria as in ovary and testes. The early 

 stages of yolk-cells resemble those of the young ova. A single 



