124 bulletin: museum of comparative zoology. 



reexamination will show that a similar arrangement of the spireme 

 threads occurs in many forms where it has not hitherto been described. 

 Even in the Orthoptera, where the polarity is in general well marked, 

 there is great variation in this respect in different species, and in some 

 cases might easily be overlooked, as it seems to have been by McClung 

 and Sutton. 



Farmer and Moore (:05) emphasize the fact that there are always 

 two distinct stages of the polar loops, which they have termed the first 

 and second contraction figures. According to these authors, during 

 the early growth period the spireme assumes the form of polar loops, 

 which are always one- half as numerous as somatic chromosomes. 

 "At the same time, the whole chromatic network contracts away from 

 the nuclear membrane, this change producing the First Contraction 

 figure. As time goes on the loops become not only increasingly 

 chromatic but also opened out again, until the apparent polarisation is 

 more or less completely lost and the nuclei present the well-known 

 coarse spirem figure within the strands of which double beading 

 or actual longitudinal fission is always more or less apparent. The 

 coarse spirem figure often constitutes a prolonged phase, but it is in 

 all cases ultimately succeeded by a short-lived and easily missed 

 resumption on the part of the split chromatic thread- work of its earlier 

 polarised arrangement; and this is followed by a strong Second Con- 

 traction and thickening of the indiAidual loops." 



It is very certain that in none of the Orthoptera which I have studied 

 are there two contraction figures such as Farmer and Moore describe, 

 nor is there at any time a continuous spireme. As I have previously 

 described in detail, the original polarity persists until immediately 

 previous to the time when the definitive tetrads are formed, and is 

 then lost by the loops becoming detached from the nuclear membrane. 

 In all cases the loops can still be seen to retain their connection with 

 the pole even after they have opened out and assumed a peripheral 

 position, while in some species the polarity is easily distinguished up 

 to the time when the loops become free. Possibly the results of 

 Farmer and Moore may be explained on the supposition that in 

 Periplaneta, where the two contraction figures are especially well 

 shown, the loops retain their connection with the nuclear wall imtil a 

 later period than in most Orthoptera. If this connection should be 

 retained until the loops begin to condense to form the tetrads, it 

 would result in precisely such structures as are figured by these 

 authors, except that between the two contraction figures the loss of 

 polarity is only appai'ent. 



