564 Theophilus s. Painter, 



authors working on the Hemiptera. Very briefly we may compare 

 them with the planosomes. 



Planosomes. Microchromosomes. 



1. Appear early in the growth period 1. Tend to condense early in the 



of the primary spermatocytes growth period and persist as 



and persist as distinct nucleoli separate nucleoli during this time 



during this period and during and in the prophase, 

 the prophase. 



2. Divide in first division. 2. Divide in first division. 



3. They show signs of division during 3. Divide in second period hut may 



the second maturation period show some irregularity in their 



but usually lag behind and are behavior at this time, 



irregularly distributed to the 

 spermatids. 



Except for the irregular distribution of the planosomes we 

 should not hesitate to call them microchromosomes, and it seems 

 very probable that the planosomes of spiders are derived from this 

 source. 



3. The third possibility that the planosomes may be derived 

 from the autosomes, which have lost their function and are degene- 

 rating, is theoretical and up to the present time no evidence has 

 been noted which would tend to support this. At the same time, 

 the study of the spermatogenesis of spiders has led me to think 

 that going hand in hand with the development of the various 

 families we have had a reduction in the number of chromosome 

 units (or autosomes as we call them). It is too early, as yet, to 

 make this as a generalization, for it is impossible to say, at the 

 present time, what should be considered as a primitive spider and 

 what a highly specialized form. Nor does palaeontology throw any 

 light on the subject. At the same time, when we arrange the 

 thirteen families studied with regard to their characters, as we 

 consider them at the present time, the less specialized have the 

 greater number of autosomes. And the presence of supernumeraries 

 suggested that these bodies might be derived from autosomes which 

 were undergoing degeneration. 



In outlining the three possibilities above, for the ctetosomes 

 and planosomes, we have not wished to exclude other possibilities, 

 such as, for example, that these peculiar bodies have arisen from 

 the cytoplasm of the cell, et ceteia. The three suggestions given, 

 seem, at the present time, the most plausible explanations of the 

 supernumeraries. So far the evidence would appear to indicate a 



