THE SPERMATOGENESIS OF LEPIDOSIREN PARADOXA. 33 
In such forms as Lepidosiren, where the resting* nucleus is 
first resolved into a tangle of leptotene threads, which can be 
traced for long distances and are found to run across one 
another in all directions, it does not seem possible to homolo- 
gise them with the daughter halves of a double spireme, and 
yet there seems no room for doubt that these are the threads 
which fuse in pairs later in zygonema. It is true that bv the 
time the zygonema is fairly far advanced we do get appear- 
ances not unlike what may occasionally (but not regularly) 
be found in the condensation of a somatic chromosome, as 
Digby has pointed out in a recent paper dealing with this 
question. To make this, however, a basis of comparison of 
somatic with meiotic prophases, to the end of denying the 
significance of parasjnidesis, is to take no account of the 
preceding stage of leptonema. 
The second foundation on which the establishment of para- 
syndesis rests, is that the spaces between the fusing leptotene 
threads (which become the longitudinal split visible here 
and there in the pachytene threads or thick spireme) is the 
space which reopens in strepsinema to form the space sepa- 
rating the two branches of the gemini, whether these are 
arranged in parallel bars, rings, crosses or other figures, and 
is the split which becomes effective in the first heterotype 
division. This is in accordance with the opinion of most 
cytologists, in opposition to the belief of Montgomery, 
Farmer and Moore, and their followers, who hold that the 
rings, etc., of metaphase I are formed by the horse-shoe- 
shaped chromosomes of the bouquet stage (each bivalent 
being formed of two chromosomes united by one of their 
ends at the apex of the horse-shoe) bending over their free 
ends in the “ second contraction ” to form the closed rings, 
figures-of-eight, or other forms met with in diakinesis. 
According to this view the longitudinal split visible in the 
early spireme is in preparation for the second division. As 
is well known, the majority of both schools are agreed as to 
the composition and further fate of the gemini once formed, 
i.e. that each is composed of two approximated somatic 
VOL. 57, PART 1. — NEW SERIES. 3 
