SOME PROBLEMS OF REPRODUCTION. 41 
V. CompParativE GAMETOGENY IN THE ANIMAL KINGDOM. 
A. Protozoa. 
1. Flagellata. 
Our chief knowledge of the gametogeny in the true Flagel- 
lata is due to the researches of Dallinger and Drysdale. 
After repeated acts of fission karyogamic unions occur, always 
binary. 
In Cercomonas Dusarpinit and TeTRAMITUS ROsTRATUS the 
gametes resemble the ordinary forms, and are isogamous. 
Bopo sALTANs is anisogamous; the larger gamete, produced 
by the longitudinal fission habitual in this species, has the 
specific form; the microgamete is smaller, and produced by 
transverse fission. Bopo caupatus and Monas DaALunceErit 
are also anisogamous, the microgamete having the same form 
as the megagamete, and only differing in size. In Dauiinenria 
Dryspauit the gametes are equal in size, but dissimilar, the 
one being like the ordinary individuals, triflagellate, the 
other uniflagellate ; so that in this group we already find ten- 
dencies to anisogamy, and indications of the specialisation of 
gametes by peculiar forms of bipartition. 
In Nocrixuca, belonging to the Cystoflagellates, conjuga- 
tion is isogamous between individuals of the ordinary type. 
In this case we shall describe the behaviour of the zygote, 
which affords a most instructive parallel to certain forms of 
spermatogeny in the Metazoa. The nucleus of the zygote 
comes to lie peripherally below an elevation of the cytoplasm ; 
and as the nucleus divides, so the cytoplasmic elevation is 
parted by crucial furrows into hillocks, into which the daughter- 
nuclei pass one to each. By some eight or nine bipartitions 
256 or 512 buds are formed, grouped into a disc-like elevation. 
By a basal thinning the buds are abstricted as uninucleate 
flagellates, while the body of the zygote is left, containing a 
residue of cytoplasm but no nucleus, and obviously incapable 
