PARTHEXOGENETIC CLEAVAGE OF THE ARMADILLO OVUM. 59 



in the anaphases of the first maturation division, which might 

 readily result in the formation of two nuclei without the extrusion 

 of a polar-body. Conditions like those shown in Figs. 2 and 3 are 

 not nearly so abundant as those like Fig. i.but they are about as 

 common as are multipolar spindles and might readily result in the 

 latter type of abnormality. Eggs with such paired nuclei have the 

 general appearance of fertilization stages but cannot be inter- 

 preted as such, unless the reunion of the polar nucleus with its 

 sister, the nucleus of the secondary ovocyte, could be considered 

 a sort of fertilization process. It is not difficult, however, to see 

 how double nuclei of this sort could form just such multipolar 

 spindles as that shown in Figs. 13 and 14. It will be readily 

 noted from the figures that these abnormal spindles have a very 

 much larger number of chromosomes than sixteen, the number 

 seen in all clear maturation figures. This in itself militates 

 against the interpretation of these phenomena as maturation 

 processes, and is in accord with the conjecture that the figures 

 may be the result of the cooperation of two nuclei derived from 

 a maturation division. 



The bipolar spindles, such as that shown in Fig. 4 (see also 

 Figs. 15 and 16), also contain more than the haploid number of 

 chromosomes and cannot on that account be maturation figures. 



EARLY CLEAVAGE STAGES RESULTING IN THE FORMATION OF A 



FEW BLASTOMERES. 



In the course of these studies several very pretty two-cell 

 stages have been encountered of which those shown in Figs. 5 

 and 6 are typical. The stage shown in Fig. 5 is a perfect two- 

 cell stage in which both nuclei are in the resting phase. There 

 are no other nucleated bodies within the zona pelucida, but 

 a pseudo-epithelium of deutoplasmic cytoids forms a capsule 

 about the two blastomeres. A clear case of a two-cell stage in 

 which the second cleavage is well under way is shown in Fig. 6. 

 The cleavage spindles are cut transversely in both cells, one of 

 which shows an early and the other a later anaphase. 



After the second cleavage the subsequent divisions are less 

 normal and the picture of blastomeric regularity is confused. 

 The spindles lose distinctness, as a rule, and the chromatin 



