A Comparative Study of the Chromosomes etc. 
277 
is equational. This is essentially the type which the Schreiners described 
for Tomopteris (’06a) and used as a model in their subsequent work. 
Other cases of parasyndesis have been described by Agar (’ll), Mont- 
GOMERY (’ll), Janssens (’05), and Janssens et Willems (’09). Janssens 
(’09) has suggested that synmixis takes place not by transfusion or ab- 
solute fusion of the double threads, but by a niethod which he calls the 
“chiasraatype”. After parasyndesis the chromosomes of a pair, in his 
opinion, twist around each other in the strepsistene stage and each beeomes 
longitudinally divided. The nodes, where the twisted chromosomes are 
in intimate contact, fuse and the internodes of the two longitudinally 
split chromosomes may become transposed from one chromosome to 
the other. His theory is based upon observations of the amphibian 
Batracoseps. It would seem, however, that the transfer of whole inter- 
nodes of chromosomes would bring about the coupling of hereditary 
characters to a greater extent than has been found in breeding experi- 
ments (Morgan ’ll). 
The insects appear to be particulary favorable objects for the study 
of syndesis and reduction; especially is this true for the groups of Ortho- 
ptera, Hemiptera and Diptera. The chromosomes are usually well de- 
fined and no such astounding discrepancies in the diploid number of 
chromosomes and the number in the first maturation spindle of a single form 
have arisen as in the case of less favorable material, such, for example, 
as Zoogonus, which has been studied by Goldschmidt (’08a), the Schrei- 
ners (’08b), Gregoire (’09), and Wassermann (’12) with widely different 
results. Cases of parasyndesis in insects have been described for Locusta 
(Otte’06; Schreiners ’06b), for Stenobothrus (Gerard ’09), for Ceutho- 
philus (Stevens ’12a), and for Euschistus (Montgomery ’ll). In all 
these cases, as in Enchenopa, the chromosomes of the last spermatogonial 
di Vision were not followed as individuals to the leptotene stage; but 
by comparison with other insects, especially Orthoptera in which each 
spermatogonial chromosome enters a small vesicle of its own (Sutton 
’02; Davis ’08; Büchner ’09) and retains its individuality, it is not 
unlikely that the leptotene threads are merely modified chromosomes of 
the last spermatogonial division. Where a fine network is formed from 
the spermatogonial chromosomes, as in Enchenopa, we cannot say, how- 
ever, that synmixis does not take place before the leptotene threads are 
formed. 
The Union of the leptotene threads does not take place in such an 
orderly manner in the insects as in the vertebrates described by Wmi- 
WARTER, the Schreiners, Janssens, and Agar. In the former there 
