The nuclear components of the sex cells of four species of cockroaches. 485 
The nucleolus of the heterotype cell is not derived front that of 
the ivnmediately preeeding soniatic cell, but arises auew in the ear- 
liest condition of the heterotype stage. 
The nucleolus of the spermatid appears to be differentiated 
directly front the chromatin of the reconstructed daughter nucleus 
immediately after the honiotype division, and the most feasible ex- 
planation of the process which follows is, that it is carried out to 
get rid of a portion of the chromatin in the spermatid.” 
Frequent reference will be made to these two publications. 
Moore, again, in connection with Arnold (’Oö) describes the chro- 
ntosomes of the first spermatocyte division of Periplaneta as present- 
ing little Variation autong themselves, as is the case according to 
their obsevvations, in phylogenetically older types.' 
Stevens (’Oö), in a discussion of the odd chroinosome in a 
number of forms, gives a Condensed account of the spermatogenesis 
of Blatta germanica. While her object is primarily to give the 
history of the odd cliromosome, other points are touched upon, which 
will be spokeu of later in the present paper. 
Finally, Wassilieff (’07) reviews the previous work on Blatta 
and contributes additional details, especially conceruing the mito- 
chondria and allied structures. The relation of the observations and 
conclusions of the writer to those of the authors mentioned in tliis 
review of literature, will be covered in the section dealing with the 
discussion of resnlts (section "Comparisons”). 
Material and Methods. 
The writer began the work with the same species, Periplaneta 
americana , which was used by Moore and Robinson. It was found 
desirable, however, to compare allied species with Periplaneta in Order 
to ■elucidate certain other points which could not be made clear ex- 
cept in the light of comparisons. 
Stglopgga orientalis, Blatta germanica and Periplaneta americana 
are all common bousehold beests and all are nearly cosmopolitau. 
Leucopluea maderice , as the name implies, is a native of Maderia, but 
vessels have distributed it to all parts of the world. In our larger 
eitles, in Bermuda, the Antilles and sürrounding islauds, it is common 
near the shipping centers. Owing to the fact that the insects breed 
throughout the year, material is available at all times and there is no 
difficulty in obtaining complete series of stages from the earliest 
