42 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
one behind the other, remain united, and a close or loose connection is 
also maintained between the two sister-segments which arise from the 
longitudinal cleavage of the chromatin threads. From each of these 
four segments four rod-like or spherical chromosomes arise by contrac- 
tion. It seems to the author most natural to regard each quadruple 
group as consisting of four single chromosomes. 
The author displays much ingenuity in endeavouring to establish 
some degree of harmony between the diverse views on reducing divi- 
sions which are at present in the field ; but we have already recorded 
many of these, and a more complete summary may be deferred until 
more facts accumulate. 
Structural Changes in Reproductive Cells of Elasmobranchs. * — 
Mr. J. E. S. Moore has made a study of the spermatogenesis of Elasmo- 
branchs. For the sake of clearness he divides that part of the reproduc- 
tive cycle which comes before the proper spermato- or oogenesis, or 
primary period, from the first and second spermato- or oogenetic series, 
in which the cellular generations precede or follow the numerical reduc- 
tion of the chromosomes. Treating first of the resting cells in the first 
spermatogenetic period, and next of the divisions of the cells of that 
period, he points out that the features of primary importance ap>pear to 
be : — (1) the existence in the resting cells of a large round nucleolus 
lying near the nuclear periphery ; (2) the evolution during the prophasis 
of division, of 24 bent chromosomes, which shorten up, and split longi- 
tudinally in half to form the same number of chromosomes in the 
daughter-cell ; (3) the existence of an extra-nuclear attraction-sphere, 
which, during this period of the spermatogenesis, is practically destitute 
of archoplasm ; (4) the consequent non-formation of an archoplasmic 
spindle-figure, and the dual origin of this latter structure, partly from 
the simple cytoplasmic radiation, partly from the intra-nuclear substance ; 
(5) the differentiation of the spindle during the dyastral figure into an 
outer and an inner fibrous sheath, which, after the escape of the parental 
nuclear sap, collapse and coalesce to form a delicate connecting thread 
between the attraction-sphere of both daughter-cells; (6) the formation 
of extra-nuclear chromatic bodies from the debris of the nuclear chro- 
matin. The rest of the transformation, or to use Mr. Moore’s term, the 
synaptic phase, between the first and second spermatogenetic periods, is 
described, and the author passes next to the divisions which occur in the 
second spermatogenetic period. The most important points appear to 
be: — (1) the transformation of the cells of the first spermatogenetic 
period into those of the second, which Mr. Moore has termed the synap- 
sis, is accomplished while the cells are in complete repose, and is marked 
by a peculiar evolution in the chromatin with the formation of peculiar 
nucleoli, and by the formation of an archoplasmic constituent round the 
centrosomes. (2) The evolution during the prophases of the first and 
second divisions of the second spermatogenetic period of twelve ring 
chromosomes, each split transversely to form the same number in the 
daughter-cell. (3) The differentiation of the spindle during the dyastral 
figure into an outer and an inner fibrous sheath, which coalesce and form 
a delicate connecting thread between the attraction-spheres of both 
* Quart. Journ. Micr. Sci., xxxviii. (1895) pp. 275-313 (4 pis. and figs.). 
