Some Problems of Reproduction: a Comparative Study of ...

26 MARCUS M. HAETOG.
Saprolegniese find a parallel in those of Dasycladus
and Derbesia (supra, p. 18).
Marshall Ward sought 1 to identify the extrusion of protoplasm
by the forming oospores with the formation of polar
bodies in the Metazoa; and the resumption of these masses he
regarded as probably connected with the alleged parthenogenesis
of the group. The latter view, and indeed the former
also, break down now that we know that both processes occur
in the formation of the asexual zoospores; they find their
explanation in the comparison with the zoospore formation of
Cladophora.
(b) Phycomycetes Aplanosporese.
The Entomophthorese present conjugation between their
hyphse; as a rule the conjugation takes place in the horizontal
tube uniting two hyphse, like the cross-bar of an H, and the
zygote forms a spherical enlargement in the middle.
Unfortunately we know nothing of the cytology of the
process in the majority of the species ; it has only been studied
in Basidiobolus, 2 which is by exception truly cellular (while
the other genera are apocytial), and which is peculiar in its
conjugation.
In this genus two adjacent cells of a hypha grow out sideways
at their adjacent ends, which turn up side by side, and
the nucleus of each enters its turned-up tip. Either nucleus
divides by mitosis; the upper daughter-nucleus passes into the
extreme tip, and is cut off as a sterile cell; the lower nucleus,
with all the protoplasm of the cell, fuses with its fellow to
form the zygote. Here we have the best parallel with polarbody
formation to be found in isogamous conjugation. If we
compare this with the conjugation of Closterium or Epithemia
(supra, p. 14) we find the interpretation obvious:
the first cells are progametes, and on approaching produce the
1
" Observations on Saprolegniese," in ' Quart. Journ. Micr. Sci.,' vol. xxiii,
pp. 282 (note) and 291.
3
By Eidam, in ' Conn's Beitrage,' vol. iii.