CHROMOSOMES IN MAN 465 



distinguished by its peculiar form and different level, from the 

 other chromosomes. It is perhaps unnecessary to remark that 

 all due precautions were taken in this case as well as others to 

 avoid confusing the chromosomes lying in adjacent cells but dif- 

 ferent sections. 



Figure 3 is from a mesenchyme cell lying directly beneath the 

 epidermis of the ventral body wall, in which the form of the 

 chromosomes differs somewhat from the preceding. At a and 6 

 are two thick heavy bars, and at e and d bodies resembling the bi- 

 valent chromosomes of th^ maturation spindles. The number is 

 thirty-four, plus a small body z which may possibly be a plas- 

 mosome fragment. 



Figure 4, a prophase of a cell in the mesothelium of the intes- 

 tine, clearly shows thirty-four chromosomes, two to which are 

 characterized by their small size and their location at opposite 

 poles of the group {1). 



Figure 6 is a prophase figure from the mesenchyme of the lateral 

 body wall in which the number of chromosomes is thirty-four. 

 Figure 7, taken from a cell in the epithelium of the nasal pit, 

 shows thirty-four chromosomes, many of them in the form of 

 large thick rods. Figure 8 is from a neighboring cell in the nasal 

 epithelium of the same section, in which the chromosomes are 

 much smaller in size but larger in number, thirty-eight. It is 

 possible that some of the chromosomes in this section are partially 

 divided as the one at d, and that some of these halves were 

 counted as single chromosomes. I have taken pains to avoid 

 such an error, and I do not believe such a mistake was made; for 

 in the case shown in figure 9, a mesenchyme cell from one of the 

 visceral arches, in which the chromosomes are characterized by 

 their small size, the number can be readily determined and is 

 found to be thirty-eight. 



In connection with figure 3, attention was called to the bilobed 

 appearance of several of the chromosomes. Delia Valla, Gregoire 

 and more recently Agar, have described similar chromosome- 

 forms in somatic mitoses. When such a chromosome becomes 

 split a tetrad-like body is formed as in figure 8, d. Hacker and 

 later Schiller have brought about the formation of typical tetrads 



