154 A. RICHARDS. 



Moniez contains much which a reinvestigation with modern 

 methods of technique will substantiate. 



As regards the method by which segmenting eggs divide, the 

 following sentences are illustrative of Child's position: 



"But although the first cleavage is usually or always mitotic, 

 there can be no doubt that amitotic division appears very early 

 in the course of cleavage. 



"Cases of mitosis are rarely seen after the first cleavage but 

 amitosis is of frequent occurrence. 



"Rarely a case of mitosis is observed: in all the hundreds of 

 eggs in cleavage stages which have been examined, not more 

 than a dozen cases of mitosis have been seen in stages later than 

 the first cleavage. When mitosis occurs it apparently always 

 involves one of the larger nuclei. Mitotic divisions of the small 

 nuclei in stages like those shown in Plate VI. have never been 

 observed. The smaller nuclei are, without doubt, dividing more 

 rapidly than the larger, and we are probably justified in con- 

 cluding that amitosis occurs in those regions of the egg where 

 division is most rapid, while mitosis is found, when it occurs at 

 all, among the nuclei which are dividing more slowly." 



With the first of these statements only can I agree. Figs. 56 

 to 63 show the successive steps in the cleavage process up to the 

 eight cell stage and every division is by mitosis. Fig. 64 show's 

 several cells from an embryo of thirty cells, among which are 

 two blastomeres in mitosis. Fig. 65 is drawn from a single 

 blastomere in an embryo of from fifty-five to sixty cells; it shows 

 an early phase of mitosis. These stages are not rare or difficult 

 to find in my material. I have examined segmenting eggs of 

 numerous other animals and do not hesitate to say that the 

 mitotic figures in Moniezia are as frequent as in other lots of 

 eggs selected at random. 1 Indeed, in five sections cut four micra 

 in thickness, in which the uterus did not contain a relatively 

 large number of eggs over twenty cases of cleavage mitoses 

 which were deemed worthy of sketching were found. In another 

 case, in 125 embryos (all that were present in the given region) 



J Of course in those cases where artificial fertilization is practical the eggs are 

 selected in the desired stage; such cases may not fairly be compared statistically 

 with the one under discussion. 



