INTRODUCTION. 23 
before further fission is carried out, or not, does not 
constitute an essential difference.” * 
Calkins remarks that while the majority of the 
Protozoa reproduce asexually, as described, reproduc- 
tion in some is bound up with complete sexual differen- 
tiation, and a series of forms may be selected which 
indicate the probable development of the sexual from 
the more primitive methods. In numerous cases the 
sexual phenomena include many of the preliminary 
maturation stages shown by the Metazoa, in the forma- 
tion of polar bodies and reduction of the quantity of 
chromatin, ete.t 
Blochmann asserted that “copulation,” in which the 
plasma-bodies of two animals become completely 
fused together to form a new individual, as well as 
“conjugation,” in which the animals, after long-con- 
tinued union, separate again from each other, and in 
which hitherto no demonstrable changes have been 
observed, actually occur. 
In all cases of fission it 1s important to note the 
part, in the process, which is taken by the nucleus. 
Invariably the first signs of division are to be noted in 
this organ ; the separation of the protoplasm, with its 
contents, into two equal parts, follows, and one half of 
the nucleus goes to complete the organisation of the new 
individual. This is, briefly stated, the process observed 
in the Amcebina. 
In the testaceous forms the process is essentially the 
same. Here division takes place by the extrusion of 
one half of the plasma-body through the mouth of the 
shell. Some remarkable phenomena have been de- 
scribed by Blochmann in the case of Huglypha alveolata. 
The protoplasm emerged from the parent-shell, and 
became covereil with shell-lamelle,t forming a new 
individual of the normal size, which received its moiety 
of the divided nucleus. But, after this point had been 
* Art. “ Protozoa” in ‘Encyel. Brit., 9th ed. 
+‘The Protozoa,’ p. 55. ‘ 
t‘ Morphol. Jahrb.,’ xiii (1887), p. 173. See Transl. in ‘Ann. and Mag. 
Nat Hist.’ (6), vol. i (1888). 
