210 THOMAS H. BKYCE. 



both mitoses, but no reduction in the number of chromosomes. 

 He holds that there is both quantitative and qualitative 

 I'eduction. His lig-iires have a strong family resemblance to 

 those in Echinus, but the chromosomes are very lumpy and 

 solid, and do not show the compound character of their 

 prototypes which I have described. Bonin and CoUiUj in a 

 recent paper on the " Mitoses in the Spermatogenesis of 

 Geophilus linearis (Koch)," also interpret the ap])ear- 

 auces as due to two successive trausverse divisions. 



This is a very good example of the extraordinary variety 

 in the manner of interpretation of closely similar appearances, 

 which is evidence of the great difficulty of reaching auy 

 degree of certainty in cases where the chromosomes are 

 small and numerous. 



I come now to another series of cases in which the so-called 

 tetrads play a large part. A figure consisting of four sepa- 

 rate spherical bodies is very rare, occurring only in Ascaris 

 and the Insecta, and can be explained in two different ways. 

 First, in Ascaris, it seems, from the researches of Boveri 

 (1897), HerLwig (1890), and Brauer (1893), that the primary 

 chromatin rods split twice longitudinally, preparatory to two 

 ra])i(lly following divisions which succeed one another with- 

 out a pause. Two groups of four rods are formed, which 

 condense into two tetrads. In the first maturation spindle 

 two of these are linked together as dyads, and pass to the 

 poles of the spindle. The dyads retained in the ovum are 

 i-esolved into monads in the second maturation division. 

 Whilst there is a mass reduction there is thus no reducing 

 division, no dissimihir distribution of the "ids" of the 

 original spireme thread. 



Second, Henking (1891) described in Pyrrhocoris tetrad 

 groups which arose in another way, by a single longi- 

 tudinal and transverse cleavage of the spireme thread, and 

 interpreted the first division as a reducing, the second as an 

 equation division. Vom liath (1892) followed this account by 

 a description of the process in Gryllotalpa, the mole-cricket, 

 in which he ligured the halves of the sjdit rods renuiining 



