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

SOME PROBLEMS OF REPRODUCTION. 27
gametes by binary fission. Owing to the subterminal position
of the nucleus in the cell at the time of mitosis one daughternucleus
has too little cytoplasm around it for further evolution,
and so forms an arrested gamete, while its sister gets
the lion's share, and enters into karyogamic union with the
(5) (O
FIG. 1.— Conjugation of Basidiobolus : a, early stage; b, division of each cell
to form active and arrested gametes; c, formation of zygote. I use
here the nuclear notation explained above.
corresponding gamete of the other pair. So we describe the
process thus : the adjacent cells are progametes, each of which
by unequal divisions forms two gametes, the apical one
arrested, the other functional.
The MTJCORINI, in the common phrase, form zygotes by the
isogamous union of gametes, save in one species, Mucor
heterogamus, Vuillemin, which is anisogamous. But this
description is not at all accurate from the present standpoint
of cytology; for "gametes" and "zygotes," so called, are
not cells, but apocytia of plurinucleate protoplasm in a cellwall,
which we may term "gametoid" and "zygotoid" respectively.
Of the nuclear changes involved in the conjugation
we know as little as in the Chytridiese. Several
possibilities are open:
(1) The nuclei of the respective gametoids may unite two
and two within the zygote in exogamous union;
(2) The nuclei may unite in pairs or otherwise, irrespective
of their origin ; or, finally,
(3) Rejuvenescence may ensue, as in plasraodial formation,