SOME PROBLEMS OF REPRODUCTION. 11 
growth failing conjugation, though the microgametes, indeed, 
are said to form but weakly plants. We know of no other 
case where a well-differentiated male cell retains this power 
of independent growth or parthenogenesis in the strictest 
sense. 
(4) Ooeamy.—This term has been freely applied to cases 
of anisogamy and hypoogamy. It is, however, better restricted 
to those cases in which the megagamete is neither ciliate nor 
flagellate, but motionless, or at the outside slightly amoeboid ; 
while the microgamete or spermatozoon is most frequently a 
free-swimming cell, and consequently retains its primitive 
mastigopod form in the majority of cases, including the highest 
Metazoa. The megagamete is usually termed an ovum or egg 
in animals; but there are profound differences, morphological 
and physiological, between the immature metazoon egg as a 
progamete and the egg after the expulsion of the polar bodies 
as a true gamete; and I shall henceforth designate the egg 
in this latter stage an ‘‘oogamete” or “oosphere,” reserving the 
words “egg” and “ ovum”? loosely for all stages. 
In most cases of oogamy the microgamete is very minute, 
reduced to a “resting” nucleus, with just enough cytoplasm 
to cover it and carry it up to the oosphere. This reduction in 
size finds a curious parallel in the reduction of the male 
Rotifer, a bag with sexual organs, and just enough other 
organs to enable him to find and fertilise the female, the organs 
of nutrition being completely absent. 
The lowest oogamous groups are certain Volvocinez 
belonging to Phytomastigopods, and the Confervoid genera 
(idogonium and Cylindrocapsa. 
(5) SipHonocamy.—Yet another mode of reproduction has 
to be noted, combined with any of the preceding, that where 
the gametes reach and unite, not by ordinary locomotion and 
as naked cells, but by a protoplasmic outgrowth of the gamete 
or gametogonium, protected by acellulose tube. This is termed 
SipHonocamy by Engler; it is a mere distinction in the 
mechanism of karyogamy, for it is associated with isogamy 
in some Conjugate, anisogamy in others of this group and 
