STUDIES ON CHROMOSOMES 373 



spect the phenomenon is different from that discovered by Bon- 

 nevie ('08, '11) in Ascaris and Alhum, where the spiral thread is 

 formed in the telophase-chromosomes and uncoils to form the 

 thread- work of the resting nucleus. 



4. The certainty that the spirals are single, not double, i.e., 

 do not consist of two interlacing spirals, as has recently been de- 

 scribed in the telojDhase-chromosomes of Trjrxalis by Brunelli 

 ('10), and in the final anaphase-chromosomes of Amphibia by 

 Schneider ('11) and Dehorne ('11). 



5. The strong evidence thus afforded that only one thread 

 arises from each chromatin-mass. 



There can, be no doubt that the process here so clearly demon- 

 strated is of the same general nature as that seen in the pre-synap- 

 tic nuclei of these animals and of the Hemiptera. I therefore 

 consider it at least probable that in the latter case also a single 

 thread is formed from each chromatin-mass and hence that the 

 number of presynaptic leptotene-tkreads is equal to the diploid 

 number of chromosomes. 



Resume of Stages a to c. The close parallel that exists between 

 the pre-synaptic stages of the Hemiptera, Odonatata and Orthop- 

 tera is obvious. In all these forms the pre-synaptic chromosomes 

 first appear in the form of massive 'prochromosome'-like bodies, 

 approximately of the diploid number, of which one {X) or two 

 (X and F) are already recognizable as the sex-chromosomes by 

 their more compact structure, regular contour, and deep-staining 

 quality. Each autosome is converted into a tightly coiled or 

 convoluted thread which ultimately unravels to form a lepto- 

 tene-thread of the stage which immediately precedes synapsis. 

 This process is clearly analogous to that seen in the spermato- 

 gonial prophases, and in each case the evidence is that a single 

 thread arises from each massive body. The pre-synaptic lepto- 

 tene-threads are thus seen to be of the same nature, and probably 

 of the same number, as the spermatogonial prophase-threads, 

 and are therefore to be regarded as forming a diploid group of 

 chromosomes. The sex-chromosomes, on the other hand, per- 

 sist in the massive form to constitute 'chromosome-nucleoli,' 



