196 MONTGOMERY A STUDY OF THE CHROMOSOMES 



The chromosomes ^ere counted in a number of pole views of the monaster stage of 

 the spermatogonia, but in most cases they were so densely grouped as to make the 

 numbers obtained very uncertain. In the most favorable case (PI. V, Fig. 234) appa- 

 rently twenty chromatin elements are present, but I could not be certain of this number. 



The relations of the chromatin nucleoli in the growth period are very puzzling. 

 On preparations stained with Hermann's saffranine-gentian violet, there appear to be a 

 variable number of rounded bodies of different volume which stain bright red ; some- 

 times they are arranged in pairs, sometimes in long chains, sometimes they show no 

 regular arrangement whatsoever. One nuclear body, much larger than the others and 

 generally irregular in outline, may be a true nucleolus. If all the red-staining bodies 

 are chromatin nucleoli, they would seem to be present in an unusually large number in 

 this species. A study of further material will be necessary to explain the nature and 

 relations of these bodies. 



BELOSTOMATID.E. 



42. Zaitha sp. 



There are two species of this genus known in the vicinity of Philadelphia where I 

 collected my material, namely, Z. fluminea Say and Z. aurantiacum (Leidy), but which 

 species it was that I collected I omitted at the time to determine. Ten testes were 

 examined.* 



In the rest stage of the spermatogonium (Fig. 235) are present two small chromatin 

 nucleoli (N. #) apposed to a large true nucleolus (N). 



Pole views of the spermatogonic monaster stage (Figs. 236, 237) show twenty-four 

 chromatin elements, of which the smallest two (N. 3} represent the chromatin nucleoli, 

 and the remaining twenty-two are chromosomes. Of the chromosomes, four are always 

 elongate and much larger than the others (t, Figs. 236, 237). 



In the synapsis stage of the growth period the twenty-two chromosomes unite to 

 form eleven bivalent ones. In the rest stage of the spermatocytes there are two uuiva- 

 lent chromatin nucleoli, sometimes joined to make a bivalent one, attached to the surface 

 of the true nucleolus. 



Pole views of the monaster stage of the first maturation division (Fig. 238) show 



* In my " Note on the Genital Organs of Zaitha " (American Naturalist, Vol. xxxiv, 1900). I described the 

 structure of these testes. To the text figure B given iu that paper, I would add now that the earlier stages of 

 spermatogenesis are to be found in what I called the " terminal fibres " at the proximal end of the testis, these fibres 

 being five long and much convoluted slender tubes which interlace together and form a rounded whitish mass at 

 the extreme proximal end of the testis ; they were not correctly represented iu the figure cited. In adult individuals 

 it is only in this portion of the testis that the earlier spermatogenetic stages occur, all the rest of the testis being 

 filled with spermatozoa. It is necessary to collect individuals in the month of May (shortly before the copulation), 

 in order to obtain the stages of the maturation divisions. 



