132 D. H. TENNENT. 



Fig. 6 shows the chromosomes of an equatorial plate of an 



Arbacia c? _, , 



—,—, . — pr esfg'. The chromosomes here are seen to be short, 



slightly bent rods. These are quite different in form from those al- 

 ready mentioned in the equatorial plate of Moira (Fig. 3), where 

 the chromosomes are longer and comparatively more slender. 



The sections of the Moira-Arbacia cross-fertilized eggs giving 

 a polar view of the equatorial plates (Figs. 7 and 8), show a 

 mixture of short and long forms probably indicating Arbacia and 

 Moira chromosomes respectively. These differences in form 

 are evident in the equatorial plates of both the first and second 

 cleavages, which is as far as I have carried the observations. 



The differences in form are less evident in the late metaphases 

 or early anaphases when the daughter chromosomes are drawn 

 out, behaving like substances with a high surface tension, and 

 then contracting during the late anaphases, into much shorter 

 rods. 



In both of the crosses, but especially in sections of eggs of the 

 Moira-Arbacia cross, an interesting phenomenon may be noted 

 (Text Fig. 2). 



In eggs in which the daughter nuclei are in the resting condi- 

 tion succeeding the first division, the cytoplasm contains many 

 deeply staining rods. The nucleus at this time does not take the 

 chromatin stain and appears like an empty vesicular structure. 



In eggs, of the same lot and on the same slides, in which the 

 fibers of the second amphiaster have begun to form, the nucleus 

 again takes the stain and shows the chromatic net, while the 

 cytoplasm is seen to be free from the bodies described. 



These structures have puzzled me not a little, but I have finally 

 reached the conclusion that the eggs in which they occur are de- 

 generating. Even though this be true it is difficult to explain 

 the simulation or perhaps occurrence of longitudinal and trans- 

 verse divisions of these chromosomes lying free in the cytoplasm. 



Summary. 

 This paper deals with observations made on sections of cross- 

 fertilized eggs of two kinds : (i) Toxopncustcs eggs fertilized with 

 Moira sperm, (2) Arbacia eggs fertilized with Moira sperm. 



