42 



CYTOLOGY 



CHAP. 



This absence of a bouquet is not, however, characteristic of insects in 

 general, for it is a conspicuous feature in many species. 



Diplotene nuclei (I) show us that each pachytene thread proceeds to 

 spUt into a pair in the same manner as we saw in the two forms already 





K 



Yi.^ 



Fig. 17. 



The formation of the meiotic bivalents in certain insects. (After Wilson, J.E.Z., 1912.) A-J, Oncopeltus ; 

 K, Anax ; h-'N, Protenor. A, B, spermatogonia! telophase; C, emergence of massive chromatin bodies in 

 spermatocyte I. ; D, E, each chromatin body (with the exception of two, the sex chromosomes) is giving rise 

 to a single coiled thread ; F, the coiled threads of E have given rise to the leptotene nucleus ; G, synizesis ; 

 H, the pachytene stage ; .the large, faintly stained body in this figure, and in figures I, J, is the plasmosome ; 

 I, diplotene stage ; J, " confused stage " ; K, three contiguous cells showing the evolution of the coiled 

 threads from the massive bodies ; L, M, N, evolution of the bivalent rings from the confused stage. 



described. Instead, however, of these pairs condensing progressively 

 into the definitive bivalents of metaphase L, the early diplotene stage is 

 immediately followed by one which Wilson calls the " confused stage " 

 (J), in which the double chromosomes lose their visible identity and 

 become merged into a vague, lightly staining reticulum. From this 



