304 Chromosomes in the Spermatogenesis of Anasa Tristis 
left periphery of the group of chromosomes of Photo. 50 there are two 
chromosomes in contact, they are nearly at right angle to each other, 
and although in close contact their individuality is by no means 
obscured. Both in the preparation and the original negative it is 
impossible to interpret these as a single chromosome and we hope their 
differentiation will not be obscured in the reproductions. We have se- 
lected for reproduction this example of a group of spermatogonial chro- 
mosomes, showing two of the chromosomes in contact, because we want 
to point out that with an unfavorable technique two such chromosomes 
would inevitably be fused into one. ~ - 
How much detail can be lost by the shrinkage of fixation may be 
appreciated by comparing, for example, the metaphases of Montgomery’s 
sketch 76 (Text Fig. 1) and Wilson’s sketch k (Text Fig. 2) with our 
photographs of the same stage on Plate II. Such a loss of detail would 
inevitably obliterate the differentiation of two chromosomes in such close 
contact as the two shown in Photo. 50. 
We should hke to point out here that we have found the demonstra- 
tion of twenty-two odgonial chromosomes in Allolobophora quite as diffi- 
cult as the demonstration of twenty-two spermatogonial chromosomes in 
Anasa. The size of the cells under investigation and the technique are 
certainly important factors in estimating the number of chromosomes. 
With pricked eggs of Allolobophora the eleven bivalents of the first 
odcyte can be demonstrated without any difficulty,” but even with this 
method the full number of chromosomes in the extremely small odgonial 
cells may often elude patient search. 
We have, perhaps, a further demonstration of these difficulties in 
Lumbricus terrestris. In Calkin’s, 95, work on the spermatogenesis of 
Lumbricus terrestris he gives the number of first spermatocyte bivalents as 
sixteen and his count has been corroborated by Bugnion and Popoff (05). 
We have not studied the spermatogenesis of Lumbricus terrestris but in 
the pricked eggs of this form we have demonstrated many more than 
sixteen perfect tetrads and we hope later to publish a few photographs 
of these preparations. 
The reality of the obstacles met by the cytologist in an effort to count 
accurately the number of chromosomes can be appreciated by recalling 
how often investigators working on the same material have arrived at 
different conclusions, disagreeing in their estimate sometimes to the 
point of doubling the number. It is impossible to appreciate these diffi- 
* Foot and Strobell, o5, photos. 116 to 150. 
ey me 
