164 GRACE MEDES. 



Collin, '01 (Geophilus line (iris) ^ Meves and von Korff, '01 (Litho- 

 bins forficatus] probably mistook for chromatin. In addition to 

 the fact that the chromosomes may actually be seen emerging 

 from the karyosphere, the achromatic nature of this substance is 

 clearly shown by its staining reaction. 



At first the chromosomes appear to lie loosely in these achro- 

 matic masses (Fig. 8), but as the threads of chromatin split, 

 becoming shorter and thicker, the enveloping substance likewise 

 contracts, staining constantly a darker brown, until when the 

 thread breaks into the smaller fragments (Fig. 11) this envelops 

 them and appears to hold them together. Soon these balls of 

 chromatin become massed more closely together in more or less 

 irregular shapes (Fig. 11, 12), but they always assume as a 

 general outline, the typical form of the tetrad (Fig. 12). This 

 particular shape is often obscured by the unequal sizes of the 

 chromatin fragments, and the distortion of the enveloping sheath 

 which, now being less diffuse, takes a considerably darker stain 

 (Fig. 13). But in all cases favorable for observation, i. t\, such 

 instances as when the whole body appears lying flat in one 

 plane, the general outline of the tetrad is plainly discernible. 



Thus it seen that while the tetrads in Scntigcra present char- 

 acteristics peculiar to themselves, still they are of the same gen- 

 eral type found in other arthropods. The only detailed descrip- 

 tion of tetrad formation in Myriapods has been furnished by 

 Blackman ('03), in Scolopendra. According to his description 

 this occurs through a longitudinal and a transverse cleavage in 

 the chromosome segments. The longitudinal division occurs 

 first, and is followed by a bending of the two halves of the seg- 

 ments at their centers, giving the first indications of the second 

 cleavage. " The short processes thus produced elongate at the 

 expense of the quadripartite segment until a cruciform figure is 

 produced, the four arms of which are of about equal length." 

 In Scntigcra, this process is naturally much obscured by the 

 breaking up of the chromosome segments into the unequal frag- 

 ments ; but when these have again become united by the con- 

 traction of the segment, the resulting figure closely resembles 

 that in a similar stage in Scolopendra. 



As the chromosomes continue to contract, the smaller glob- 



