Spermatogenesis in spiders. 541 



have convinced me that there is no definite association between any 

 particular autosome and supernumerary body. If a supernumerary 

 lies close to an autosome, as in Fig'. N, it is just a matter of 

 chance and implies no relation of the two. During- the early 

 prophase the centrosomes take up their position on opposite sides 

 of the nucleus. In Fig-. 0, are shown the two centrosomes of one 

 cell as they appear at this time. The centrosome marked "a", is 

 made up of two unequal parts, while the centrosome marked "i", is 

 made up of two bodies of equal size. We find the same appearence 

 of the ceutrosome throughout the maturation divisions. 



Late Prophase and Early M etap hase. After the nuclear 

 wall has dissolved the autosomes are drawn into the spindle of the 

 first maturation division. The general appearance of such a spindle 

 is shown in Fig. 71. 



In Fig. 71, we have the accessory chromosome composed of two 

 rod-like elements lying side by side. The more typical appearance 

 of this body, however, is shown in Figs. 72 and 73. Here, viewed 

 from the side, the accessory appears as a single rod and we find 

 attached to it three smaller bodies. In the case of the cell shown 

 in Fig. 73, "6", only two of these show. 



This association of three small bodies with the accessory 

 chromosome is very constant and may be seen in the majority of 

 the cells. Now and then, however, the accessory elements are 

 placed in such a waj^ as to hide part or all of the small bodies. 

 The typical number and arrangement is shown in Fig. 72 and 73. 



The accessory chromosome passes undivided to one pole early 

 in the metaphase (Fig. 74) and the ctetosomes, for such is the nature 

 of the small bodies attached to the accessory, pass with it, without 

 showing any sign of division. As the accessory approaches the 

 centrosome, however, the ctetosomes tend to become detached from 

 it and they are often found lying free next to the latter. 



Two points of interest are to be noted about the hétérochromosome 

 elements. The most striking, perhaps, is the definite association 

 which these supernumeraries show for the accessory chromosome. 

 These bodies are closely similiar in their behavior to the ctetosomes 

 found in the gray variety of Maevia vittaia, but there is one important 

 point of diiference which should be emphasised. In Maevia only one 

 half of the primary spermatocytes carry the ctetosomes, while in 

 AmauroUus, all of the primary spermatocyte cells seem so carry 

 them, as far as it has been possible to determine. It should be 



Zool. Jahrb. XXXVIII. Abt. f. Anat. 36 



