REPRODUCTION OF PROTOZOA. 117 
either permanently or'temporarily. This is an incipiently 
sexual process; it is the azalogue of the fertilisation of an 
ovum by a spermatozoon. In many cases, moreover, 
there is a difference between the two conjugates, analogous 
to the difference between ovum and spermatozoon. 
(1) It is one of the recurrent phases in the life history of some of the 
simplest Protozoa (Proteomyxa and Mycetozoa) (see p. 107), that a 
number of amceboid units flow together into a composite mass, which 
has been called a ‘‘ plasmodium.” ; 
(2) It is known that more than two individual Sporozoa and other 
forms occasionally unite. To this the term ‘‘ multiple conjugation ” 
has been applied. 
(3) Commonest, however, is’ the union of two apparently similar 
individuals, either permanently, so that the two fuse into one, or 
temporarily, so that an exchange of material is effected. Permanent 
conjugation has been observed in several Rhizopods, Infusorians, and 
Sporozoa. ‘Temporary conjugation is well known in not a few ciliated 
Infusorians, and it is possible that a curious end-to-end union of certain 
Sporozoa is of the same nature, or it may be of the nature of a 
‘‘plasmodium ” formation. The formation of small spores (gametes) 
which conjugate is not uncommon. 
(4) There are some cases where one of the conjugating individuals 
is larger and less active than the other. Thus in Vorézcella, a small 
free-swimming form unites and fuses completely with a stalked indivi- 
dual of normal size. This ‘‘dimorphic conjugation” is evidently 
analogous to the fertilisation of a passive: ovum by an active sper- 
matozoon. In Volwox this is even more obvious, for the small: and 
active cells, both in shape and method of formation, recall the sper- 
matozoa of higher fornis. : 
Significance of Conjugation.—The precise interpretation of 
conjugation is uncertain. We may regard it as a mutual rejuvenescence, 
each unit supplying some substances or qualities which the other lacks ; 
or we may regard it rather as a process by which the average character 
of the species is sustained, peculiarities or pathological variations of one 
individual being counteracted by other characters in the neighbour 
(apparently no near relation) with which it conjugates ; or we may see 
in it a source of variation as the result of new combinations among 
the essential hereditary substances. The researches of M. Maupas have 
thrown much light on the facts, and some of his results deserve summary. 
It has been often alleged that the subsequent dividing is’ accelerated 
by conjugation ; but Maupas finds that this,is by no means the case. 
The reverse in fact is true. While a pair of Infusorians (Onychodromus 
grandis) were engaged in conjugation, a single individual had,. by 
ordinary asexual division, given rise to a family of from forty thousand 
to fifty thousand individuals. Moreover, the intense internal changes 
preparatory to conjugation, and the general inertia during subsequent 
reconstruction, not only involve loss of time, but expose the Infusorians 
to great risk. Conjugation seems to involve danger and death rather 
than to conduce to multiplication and birth. 
