Elements of comparative anatomy (1878) Elements of comparative anatomy elementsofcompar00gege Year: 1878 PROTOZOA. 87 tions of sexual differentiation. They always propagate, therefore, by modes which are called asexual, among which the chief part is played by fission and generation. The nucleus appears to be of great importance in all their modes of multiplication. Spores have been observed to be formed within the organism in Rhizopoda. A larger or smaller part of the protoplasm of the body is used in forming them ; when a larger portion is used this mode of multiplication is allied to that m
Elements of comparative anatomy (1878) Elements of comparative anatomy elementsofcompar00gege Year: 1878 PROTOZOA. 87 tions of sexual differentiation. They always propagate, therefore, by modes which are called asexual, among which the chief part is played by fission and generation. The nucleus appears to be of great importance in all their modes of multiplication. Spores have been observed to be formed within the organism in Rhizopoda. A larger or smaller part of the protoplasm of the body is used in forming them ; when a larger portion is used this mode of multiplication is allied to that mode which is so common among the Protista, in which the whole body breaks up into a number of spores, and so multiplies by division. In the Radiolaria the contents of the central capsule are active in reproduction. The nuclei in it become surrounded with protoplasm, and form flagellate swarm- spores. The mode of reproduction is most exactly known in the Gre- garinas. As a rule multiplication commences by the concrescence of two individuals; this generally occurs very early, so that the two individuals, which form one body, the anterior end of one being attached to the posterior end of the other (Fig. 29), go on growing for some time; or conjugation may only take place later, when the forms are mature. After this comes a condition of rest, accompanied by encystation, in which the two individuals form a rounded body, with a partition between them. Then the partition disappears, and the substance of the body, and also the nucleus, breaks up into an amorphous mass, from which numerous vesicles gradually arise. From these latter a number of germ corpuscles, called ' Pseudonavicellas,' on account of their shape, are formed. These gradually fill the whole cyst, and each gives rise to a single very small organism, consisting of protoplasm solely, and this, being without a nucleus, corresponds to a cytod. Each of these structures moves about in an amoeboid manner, and is gradually diffe
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