320 PROCEEDINGS OF THE ACADEMY OF [April, 



sexes, though because of certain peculiarities of behavior the equal 

 pair of idiochromosomes may be considered as representing different 

 characters, so that the dimorphism, though masked, may nevertheless 

 be considered present in this class also. 



The question arises, can the species of Lepidoptera here studied be 

 brought into relation with the theory of dimorphisni and individuality 

 of the chromosomes? 



A careful examination of the chromatin element in the species here 

 described shows, as has already been pointed out, that one chromatin 

 element acts differently from the others during a certain period in 

 the development of the germ cells. It Is distinguished from all other 

 cell structures by its staining reaction, its precocious division, and its 

 close association with a plasmosome; while later it shows likeness to 

 the other chromosomes in form, valence and division; such behavior 

 makes it necessary to interpret this, as other workers have done, as 

 an equal pair of idiochromosomes representing different characters 

 from those of the other chromosomes and expressing by their peculiar 

 behavior a masked dimorphism. 



The present study of Lepidoptera offers no such support to the 

 theory of the individuality of the chromosomes as Sutton found in 

 Brachystola and other workers have found in Hemiptera, yet the 

 following facts are evidence in favor of this theory; (a) that the 

 number of chromosomes remain the same from generation to genera- 

 tion, (6) that they are seen in maturation divisions to be formed of 

 pairs of equal size, (c) that in smear preparations the boundaries can 

 be traced and the chromosomes never entirely lose their continuity 

 during the growth stage, and (d) that at least one of the chromatin 

 elements shows marked peculiarity in its behavior, and can therefore 

 be traced throughout the growth period. These facts show that 

 Lepidoptera like the other insect orders may be brought into harmony 

 with recent cytological work. 



V. Summary. 



1. The spermatogonia contain an equal number of chromosomes 

 of about the same size and shape, and in the family of Saturnids a 

 net knot of chromatin granules is always found during the resting 

 stage. 



2. During the growth period of the spermatocyte a dense body is 

 found which is either single or dumbbell shape, is eccentrically placed, 

 and stains like basi-chromatin ; in T. polyphemus and A. io it first 

 appears in the early post-synapsis stage, though in other species it is 



