SPERMIOGENESIS OF HELIX ARBUSTORUM. 
329 
period preceding the division. So it is intelligible that we find chromo¬ 
somes twice during the development of the spermatocytes : they form 
themselves in synapsis, because the cell prepares to division, but they 
disappear in the next stage because division does not take place, and 
reappear again when the cell prepares for the second time to division, 
and then retain their individuality, because the division now really 
takes place. 
5. The heterochromosomes. 
Heterochromosomes, as is well known, are characteristic of the 
germ-cells of the Tracheata. Besides this group only one animal is 
known which certainly has heterochromosomes, i. e. Helix nemoralis, 
from which they have been described by Ziegler (130). The second 
case is that of H. arbustorum. 
The heterochromosomes are, as a rule, well distinguishable from 
the ordinary chromosomes during the development of the spermatogonia 
and spermatocytes. It is otherwise in H. arbustorum, therefore my 
observations referring to them are fairly defective. I have had the 
opportunity of observing them only in the first maturation spindle and 
in the phase immediately preceding the formation of the spindle. In 
the latter mentioned phase a spherical chromosome of smaller size is 
to be found among the ordinary ones (Pl. VIII., Fig. 1). This chromosome 
divides during the first maturation division into two parts. The daugh¬ 
ter chromosomes lie symmetrically in the spindle (Pl. IX., Figs. 6., 8.) 
and pass into different daughter cells. They are also regularly spherical 
in shape, and are considerably smaller than the ordinary chromosomes. 
I have not had the opportunity of observing them during the second 
maturation division with any certainty, though I have found even during 
this division chromosomes smaller than the others, but they were never 
in such a characteristic position as to make it possible to determine 
whether they were heterochromosomes, or parts of ordinary chromosomes 
cut away. Nor have I had the opportunity of finding them in the sper¬ 
matogonia. 
Upon the base of these defective observations it is undeterminable 
to which group of heterochromosomes they belong. Their characteris¬ 
tically small size would perhaps point to their belonging to the m-chro* 
mosomes of Wilson. Naturally, it is also not quite certain that they 
belong to the diplosomes at all, but it may be considered probable, 
because Helix nemoralis has diplosomes, and according to the resear¬ 
ches, it can be regarded as a rule that species belonging to the same 
systematical category have the same kind of heterochromosomes. 
