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that largely have to do with questions of priority, to consider more 

 important points at issue between us. I found sex -cells to occupy a 

 horseshoe-shaped zone, with the two lateral limbs connected by a zone 

 of cells lying behind the caudal end of the embryo. Dustin categori- 

 cally denies that any sex-cells are to be found caudal to the embryo. 

 He has thus failed to find a large proportion of them. Here is a point 

 at issue in which one of us is right and the other wrong. While it is 

 not a fundamental point in theory, it is one that is of vital importance 

 in affording a basis of judging the accuracy of the results of our counts 

 of the total number of sex-cells present in the embryo. Dustin finds, 

 on the average, a far smaller number of sex-cells than I did, although 

 his highest figures are above my lowest counts. 



Dustin offers to explain the differences in our observations by the 

 same old suggestion that I must have mistaken cells about to undergo 

 mitotic division for sex-cells. Without wishing to appear ill natured, 

 iet me say that I feel quite as well able to distinguish sex-cells as is 

 my honored colleague. Dr. Dustin. A recent examination of my material 

 has merely confirmed my earlier observations. I have made a number 

 of series of sagittal sections which show, with the utmost clearness, 

 masses of sex-cells lying caudal to the embryo and so distributed as to 

 complete the "bend in the horseshoe". These cells are recognizable, 

 not alone by reason of their large size and rounded shape, but by the 

 presence of the medium sized yolk spherules so characteristic of the 

 sex-cells of this form. Their presence in this region is so unmistakable 

 that any one at all familiar with sex-cells can find them at a glance in 

 my series of sagittal sections. I am so certain of my position that I 

 shall be not only willing, but very glad to loan a series of such sections 

 to any responsible person who may be sufficiently interested in this 

 controversy to send for it. 



My material is all stained with Heidenhain's iron alum haemato- 

 xylin, which colors the yolk granules a deep black. Since the character 

 of these is the most distinctive feature of the sex-cells, the importance 

 of a stain that will bring them out sharply is obvious. Now Dustin 

 states that his material was stained with borax carmine and with 

 haematoxylin and eosin. Neither of these stains is so well adapted to 

 this work as is iron alum haematoxylin. I should think that it would 

 be especially difficult to attain precise definition of these cells with 

 borax carmine. 



Since Dustin has utterly failed to find the sex-cells of Chrysemys 

 throughout a very large extent of their zone of distribution, the results 

 of his counts can have no value. He gives tables in which the numbers 

 of sex-cells in 10 specimens of Chrysemys are stated. Since these 

 specimens are indicated in the tables only by their serial numbers, 

 without any statement as to size, one is forced to guess roughly at 

 their stage of development by comparing these serial numbers with 

 those used to designate stages described elsewhere in the text. The 

 author has not stated whether certain embryos of similar measurements 

 were taken from the same nest. He, furthermore, does not indicate 

 the distribution of the sex-cells throughout the embryo, although such 



