ATS Mr. L. Doncaster. [Jan. 25, 
while elsewhere in the same egg the full diploid number (20) was clearly 
present. 
In the spring of 1910 I collected series of eggs from a large number of 
females, and from them obtained nineteen series of sections of well- 
preserved eggs, averaging about 27 eggs from each female, besides several 
smaller or less well-preserved series. Since the rate of development had 
proved rather variable in previous years, these were fixed at various ages, 
and not all the series show every stage from the undivided egg-nucleus up 
to segmentation divisions in which the chromosomes can be counted. Since, 
however, most of the series included eges between two and six hours old, 
the majority show most of the stages desired, and several series are very 
complete. A comparison of the various series shows at once that they 
mostly fall into two groups: some show the diploid number (20) of 
chromosomes whenever the segmentation mitoses are clearly countable, 
and these never contain groups of polar chromosomes in the segmentation 
stages ; others show the haploid number (10) in segmentation divisions, and 
in these a double or triple group of polar chromosomes can be found at the 
edge of the egg in nearly every specimen in which the sections are complete. 
Out of the nineteen series of eggs, five series are of the first type, containing 
diploid segmentation divisions and no polar chromosomes, while one other 
series, though containing only one egg with a recognisable mitosis, belongs 
to this type from the complete absence of polar chromosomes in the early 
segmentation stages. Of the second (haploid) type, seven series of eggs 
show undoubted polar mitoses or polar chromosomes; in two of these 
segmentation mitoses occur which are certainly haploid, and in two others, 
though the chromosomes cannot be counted accurately, the mitoses are 
almost certainly haploid. In the other three series there are no segmentation 
mitoses at a stage when the number of chromosomes can be estimated. 
Judged by the presence or absence of polar chromosomes, therefore, there 
are six series of the unreduced and seven of the reduced type; five of the 
former show diploid, two of the latter certainly haploid, segmentation 
mitoses. In the series of eggs collected in- 1909 the proportion of the 
diploid type was probably greater. In the remaining six of the 1910 series 
all the eggs are too young to be classified with confidence. The fact that 
only two out of seven haploid series contain eggs with undoubted haploid 
segmentation mitoses, may seem insufficient evidence that eggs containing 
polar chromosomes have reduced segmentation nuclei, but it must be 
remembered: (1) that in none of the eggs with diploid mitoses can polar 
chromosomes be found, and (2) that every egg in which the sections are all 
complete shows polar chromosomes when the mitoses are haploid. In some 
