178 Papers from the Marine Biological Laboratory at Tortugas. 



the appearance as demonstrating, Gutherz as contradicting, the presence of 

 an accessory. My own figures occasionally show a double chromosome at 

 one pole in advance of the main complex, and the evidence favors Guyer's 

 interpretation rather than Gutherz's, but there is here nothing so striking 

 as one sees in certain insects (e. g., the phasmid, Aplopus mayeri) and the 

 opossum. Strong evidence for the presence of a heterochromosome in 

 man is given by Gutherz in his illustrations of early postsynaptic nuclei 

 (text-figs. 2 to 6). But neither he nor Guyer seems to offer satisfactory 

 evidence as to its composition from chromosome counts and behavior at 

 metaphase. Both, moreover, regard it as a double structure. My own 

 evidence confirms the findings of Guyer and Gutherz in so far as pertains to 

 the actual presence and bipartite nature of a heterochromosome or X-ele- 

 ment, and it emphasizes the additional points of similarity between this 



Fig. I.— Human primary spermatocyte; nucleus in early diplotene post-synaptic phase, showing a deeply 

 staining oval chromatin (chromosome) nucleolus on the nuclear wall and attached to one of the threads; the 

 true nucleolus is a spherical, less deeply staining body, and only very rarely placed close to the nuclear wall. 

 The cytoplasm is homogeneous, finely granular. . , ... r »t,„ i,„*»,«^t,,„ 



Figs. 2 to o.— OutUnes of nuclei at same stage to show the general form and location of the heterochro- 

 mosome. It is almost invariably bipartite and attached to one of the threads, and on the nuclear membrane. 

 The nucleolus when present is indicated in outline. 



and undoubted sex-chromosomes, namely, frequent connection with the 

 diplotene thread and close spatial relationship to nuclear wall (exception, 



text-fig. 3). 



Judging from the illustrations, Winiwarter (191 2) has had the advantage 

 of possessing by far the best human material. His illustration (fig. 25) is 

 practically a duplicate of my own of the postsynaptic diplotene (passing 

 into the pachytene) phase. However, the later history of the accessory 

 element as traced by Winiwarter is not at all stages perfectly clear. But 

 figures 39 and 40 show pairs of sister spermatids, one pair with, the other 

 without, a deep-staining nuclear body (accessory chromosome?). If this 

 spermatid element actually represents, as seems very probable, the postsyn- 

 aptic nuclear bipartite body, or heterochromosome, then cogent additional 

 evidence here also accrues favoring the legitimate interpretation as a 

 heterochromosome of the similar (structurally and tinctorially) peculiar 

 postsynaptic nuclear element wherever found in mammals. 



