70 Proceedings of the Royal Physical Society. 
VII.—Some Points in the Cytology of the later Spermatogonial 
and First Meiotic Nuclei of Fasciola hepatica (Distomum 
hepaticum). By Monica Taylor, 8.N.D., B.Se. 
(Read 27th March 1916. MS. received 27th March 1916.) 
(With. Plates.) 
It has been occasionally urged by cytologists that a pairing of chromosomes ~ 
takes place in the latter half of the last spermatogonial division (Montgomery, 
Sutton, Stevens, Dublin) (3, 2), but literature dealing with the full history 
of the nuclear changes that take place in the interval that elapses between 
the last spermatogonial anaphase, and the spermatocyte I. prophase, is very 
scanty. In work, the completion of which has been interrupted by the 
war, Dr Agar found, that in Lepidosiren, the thirty-eight chromosomes of 
the last spermatogonial metaphase apparently pair into nineteen in the 
telophase. The spermatocyte I. resting nucleus in Lepidosiren is therefore 
constituted out of nineteen paired chromosomes which reappear as the 
nineteen pairs of leptotene threads in the beginning of the first meiotic 
prophase. As the seriation of the nuclei at this point is rather difficult in 
Lepidosiren, Dr Agar asked me to examine this stage of the premeiotic 
processes in Fasciola hepatica, since for any study of this sort it 1s necessary 
to have some very definite criterion for distinguishing the different generations 
of spermatogonia—Mi§x Dingler, in a paper entitled “ Uber die Spermatogenese 
des Dicrocoelium lanceatwm (Distomum lanceolatum)” (1), had demonstrated 
topographical relations which, if true for the genus, would make Fasciola 
hepatica very useful in this respect. In older specimens of Dzerocoeliwm 
(Distomum lanceolatum) the walls of the gonad, which is a much branched 
tubular organ, contain spermatogonial elements only. The cells containing 
“maturation” nuclei lie in the cavity of the gonad. This arrangement has 
been brought about as follows:—One spermatogonial nucleus gives rise by 
successive divisions to a group of eight nuclei. These eight nuclei then 
prepare for the first meiotic division and give rise to a group of sixteen nuclei. 
These sixteen in turn produce a group of thirty-two spermatid nuclei which 
eventually become the nuclei of the long thread-like spermatozoa. It is 
at the eight-nuclei stage that the group of cells loses its connection with 
the walls of the gonad and passes into the central cavity, there to undergo 
its subsequent conversion into thirty-two spermatozoa. Hence, by shaking 
out the contents of the gonad tubes, only cells undergoing the maturation 
divisions escape, and by examining the number of cells in the group the 
“spermatogenic position” of the nucleus can easily be determined. And on 
