"ACCESSORY CHROMOSOME' IN EPEIRA. 195 



I am greatly indebted to Professor Wilson for assistance in 

 directing this work, and in the preparation of this paper. I wish 

 also to thank Professor Calkins for his kindness in correcting the 

 manuscript. 



TERMINOLOGY, METHODS, ETC. 



At Professor Wilson's suggestion I shall designate the " acces- 

 sory chromosome " as the " odd chromosome," a name first used 

 by Montgomery in a somewhat different sense. 1 Since there 

 is no reason for calling it the " accessory chromosome," and since 

 it behaves heterotropically in only one division, it seems advisable 

 to adopt the simpler name, with the important significance that it 

 has no mate throughout the history of the male germ cells. 



Material was obtained in August and September, 1905, and 

 also again in the early spring of 1906. The testes were dis- 

 sected out rapidly in the fixing fluid, instead of the customary 

 normal salt solution, as the process was thus rendered much 

 easier. Strong Flemming gave the best fixation, and the finest 

 results for general study were obtained with iron haematoxylin 

 and pure saffranin, the latter giving especially beautiful and val- 

 uable results. Several different stains were tried as a differential 

 test for a plasmosome, thionin, Auerbach and Flemming-triple. 

 Long-extracted iron haematoxylin slides were studied also, but in 

 no case could I find any trace of a plasmosome. 



The figures for this paper are camera drawings made with a 

 compensating ocular, No. 12, and a J y oil immersion lens. 

 They were enlarged 2y 2 diameters with a drawing camera, cor- 

 rected from the original, and then reduced one half in the final 

 plates. 



SPERMATOGONIAL CHROMOSOMES. 



Longitudinal sections of the testes give a complete series of 

 stages from the resting spermatogonia around the periphery to 

 the ripe spermatozoa in the central lumen. For this work it 

 did not seem necessary to make a detailed study of the sperma- 

 togonia, the one important thing being to determine the number 



1 In his latest paper ('06) Montgomery recognizes the fact that there is no distinc- 

 tion between the "odd chromosome" and the accessory, as was pointed out by 

 Wilson ('05). Montgomery now proposes the term " monosome " for this chromo- 

 some. 



