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

74 MARCUS M. HARTOG.
zygote in the same or allied forms. Logically, of course, all
these being processes of rejuvenescence should have been
treated earlier, but the foregoing discussion was necessary to
the full understanding of the analysis of paragenetic phenomena
which I now proceed to give.
1. TRUE PARTHENOGENESIS we define as the development of
a single unfertilised (facultative) gamete. It occurs in the following
cases:
a. ISOGAMETES.—Not infrequently facultative.
b. MICROGAMETES.—Only known to be facultative in Ectocarpus;
the reduction of cytoplasm is too heavy a disadvantage
for the resumption of active cellular life.
c. MEGAGAMETES are more frequently facultative in the
lower Algse and in Chara crinita. In other Metaphytes
parthenogenesis is unknown. The only cases of true parthenogenesis
of the Metazoan oosphere, differentiated as such
by the formation of both polar bodies, are the following
—Liparis dispar and some other Lepidoptera, and Apis
(Drone eggs).
2. SIMULATED CELLULAR, PARTHENOGENESIS occurs when a
vegetative cell that might otherwise have formed a gamete
assumes directly the behaviour of a zygote (" azygospores" of
Conjugatse, " auxospores" of certain Diatoms).
3. SIMULATED APOCYTIAL PARTHENOGENESIS occurs when an
apocytial gametoidassumes the behaviour of a zygotoid ("azygospores"
of Mucorini).
• 4. PROGAMETAL REJUVENESCENCE occurs when a progamete
assumes the behaviour of a zygote. This is stated to be the
case in many Arthropods where the ovum, after the expulsion
of one polar body only, develops without fertilisation. According
to the recent discoveries of O. Hertwig and Boveri,
many cases referred to this (if not all) should be placed under
the following heading.
5. METAGAMETAL REJUVENESCENCE is the best term I can find
to fit the case of certain flowering plants (Coelebogyne,
Citrus, Funkia, Nothoscordum), where the tissue-cells
adjoining the apex of the embryo-sac grow into it, and