278 THOS. H. MONTGOMERY, 



IX. General part. 



1. Relations of chromatin and linin; the chromosome concept; 

 individuality of chromosomes. 



2. Movements of the chromatin. 



3. Polarity of nucleus and cell body. 



4. The synapsis stage. 

 Literature list. 

 Explanation of plates 19 — 25. 



Introduction. 



The present study was undertaken with two main objects in view. 

 First, to find whether or not Terijjatus, which is generally held to be 

 in the ancestral line of Insects, would show a type of spermatogenesis 

 similar to that of Insects. And second, to determine whether in Peri- 

 patus there would be a clue to the mode of origin of that curious 

 metamorphosed chromosome, first fully described by me for Penfatoma, 

 and termed the chromatin nucleolus. My work has shown that Peri- 

 patus does not possess a chromatin nucleolus, so that the search for 

 the first phylogenetic appearance of this body must be made upon 

 other fonus higher in the Arthropod series. But this study does show 

 that the process of spermatogenesis in Peripafus is very similar to 

 that of Insects, Further, Peripatus has proven to be a favorable 

 object for cytological work in a number of ways, especially in the 

 clearness in which it shows the series of changes of the synapsis 

 stage. 



This similarity of the spermatogenesis in Insects and Peripatus 

 is an important one. It suggests the working hypothesis that com- 

 parative studies may lead to an understanding of the phylogeny of , 

 chromatin reduction and other fundamental cell phenomena; and that j 

 from such work it may yet be possible to deduce what may be termed I 

 a "cytological classification" of animal forms. Long and patient in- 

 vestigation will be necessary to test the validity of this hypothesis, 

 for our present facts are too few to allow broad generalisation. But 

 surely the time has come when the study of cytology can be brought 

 more in touch with the broad field of comparative anatomy, and the ii 

 two work together as one in the attempt to consummate the highest ' 

 aim of zoological investigation, the expression of the facts of structure 

 in terms of phylogeny. 



The work done hitherto to express cellular phenomena phylo- r 

 genetically has taken into account principally the centrosomes and | 

 central spindles. But I think that these structures are too readily 



