132 CHROMOSOMES IN THE SrKKMATOGENESIS OF THE HEMIPTERA HETEROPTERA. 



blance in form and size to the single idiozome body of Pcripuliis ; and they are 

 probably masses of idiozome substance, well defined and few in number, whereas in 

 most of the Hemiptera this substance is usually more or less diffused in a zone con- 

 centric to the nucleus. In the synapsis stage there is a single large mass of this 

 substance at the distal pole of the nucleus. 



First Maturation Division. — There are always 13 elements (Fig. 256), one more 

 than half the number in the spermatogonium, therefore 2 of them must be univalent 

 and the others bivalent. They show ratlier a dense grouping. The largest 2 {A, a- 

 B, h) correspond to the 2 largest pairs of the spermatogonium, and are usually placed 

 in the middle of the chromosomal plate ; 2 smallest elements always lie on the peri- 

 phery, the smaller of which {K, k) probably represents the smallest pair of the sperma- 

 togonium. All divide in this mitosis so that the second spermatocyte receives also 

 13 chromosomes. 



Second Maturation Division. — Here the chromosomes are grouped differently in 

 the spindle (Fig. 258), namely, as a circle of 1 1 around a central pair. The latter is 

 composed of a smaller {Di) and a larger (<//) body placed one above the other, and 

 these move apart into opposite spermatids before the other chromo.somes divide (Fig. 

 257) ; these 2 are obviously the unequal elements of the spermatogonia, and each of 

 them must have undergone an equational division in the preceding mitosis and have 

 been vuiivalent there. The smaller component of this bivalent diplosome, I)i, is ne.Kt 

 larger than the smallest of the autosomes, A'^, k, while the larger, (//, is, counting from 

 the smallest, the fourth in'size of all the elements; these size relations probably hold 

 true for the preceding division, and by means of it we can detei'mine which elements 

 of the former chromosomal plate (Fig. 256) are these elements Di and di. Each of 

 the 11 autosomes divides, so that each spermatid receives 12 elements in all ; this is 

 t(j be determined from the form of the chromosomes and their position in the spindle 

 (Fig. 257), for they are too densely crowded in the spermatids to be determined there. 



Literalihre. — My preceding account (1901/>) was entirely correct, except that by 

 a slip of the pen I stated that the second spermatocyte receives only 11 chromosomes; 

 I did not describe the second maturation mitosis. 



HYDROBATIDM 



36. Hygotrechus sp. 



Spermatogonic Division. — There were only four good pole views. In three of 



them 20 elements could be counted, Imt in the fourth, which was the clearest because 



the chromosomes were most fully separated, 21 were found (Plate XIII, Fig. 259). 



Twenty of these are seen to form 10 pairs (.1, a-J, j), which vary to considerable extent 



