Spermatogenesis in spiders. 561 



reaction for a number of diiferent stains, it should be considered 

 as a chromosome, if we accept Wilson's definition. 



Turning to the spiders, let us see how far the small bodies 

 found in the spindle of many diiferent families conform with these 

 requirements. It must be clear from the description which has been 

 given of the ctetosomes and planosomes, that they show every 

 characteristic required. The planosomes may divide as has been 

 shown. In a great many cases it is possible to see that they are 

 connected by spindle fibers to the centrosomes of the cell. And it 

 has been possible also to follow their course through both of the 

 maturation divisions. So that whatever view we may hold for these 

 small bodies, whether we regard them as bodies which have a 

 function, or had a function which has been lost, we must still regard 

 them as chromosomes in every sense of the word. 



Before going further, I wish to emphasize that there are very 

 important differences between the ctetosomes and planosomes. Both 

 types of chromosomes are found in Amaurohius sylvestris. In the 

 case of the ctetosomes we find that they are invariably associated 

 with the accessory chromosome during the first maturation division, 

 and pass undivided with that body to one pole of the cell. 



The planosomes do not show any relation with the accessory 

 elements but act as independent chromosomes; they may or may 

 not divide, and their ultimate distribution is very irregular. 



At first sight this division into ctetosomes and planosomes may 

 seem arbitrary, but after a study of thirteen families of spiders, 

 I have been led to believe that these two types of bodies are 

 fundamentally different, not only with regard to their behavior but 

 in their origin as well. We have two types of bodies in the two 

 varieties of Maevia vittata. Below is given a summary of the points 

 of similarity and difference, shown by the ctetosomes and plano- 

 somes. 



Ctetosomes. Planosomes. 



1. Appear in the rest period of the 1. Appear in this rest period. 



first spermatocyte. 



2. Fuse with the accessory chromo- 2. Fuse with the accessory chromo- 



some elements during this rest some elements during the rest 



period. period. 



3. Do not separate from the accessory 3. Always separate from the accessory 



chromosome during the growth chromosome elements during the 



period. growth period. 



