172 



THE PROTOZOA 



apparent as in the free-swimming species, as, for instance, in 

 Acinetaria, where conjugation can take place between two adjacent 

 individuals each on its own stalk. But in the Vorticellids special 

 free-swimming individuals, microconjugants, are developed which 

 are budded off from a sedentary individual, and then acquire 

 cilia, swim off, and conjugate with another sedentary individual 



(Fig. 78). It seems obvious that this 

 state of affairs is an adaptation to the 

 exigencies of a sedentary life to insure cross- 

 fertilization analogous to the formation of 

 complemental males in the Cirripedes. The 

 free - swimming microconjugants of Vorti- 

 cellids are commonly termed " males," but 

 it is open to question whether, strictly 

 speaking, they deserve that title. 



It is in species with marked differences 

 between young and adult forms that the 

 greatest differentiation of the gametes 

 occurs, though by no means universally even 

 in such forms. In polymorphic species of 

 this t3 r pe, three different conditions can be 

 distinguished, to which reference has been 

 made in the previous chapter. 



FIG. 78. Vorticella \micro- \ Macrogamy that is to say, syngainv 

 stoma, Ehrb. On the left , , ..,? . ,. ., , /A. ' " 



an ordinary, sedentary between lull-grown individuals of the species. 



individual (macroconju- In this type the gametes appear to be always 

 gant) with two microcon- f ,, -aimi'lar QH far ns iq known PX 



juganta (m.c.) attached P e lar ' so as 1S Known > es> 



to it, one of which (to amples are seen in Actinophrys (Fig. 71), 



the left) is in the act of th c hromidiogamy of Arcella (Fig. 80), and 



conjugation. On the & J 



right is an individual possibly NoctllUCd (p. 279). 



with the stalk contracted . Microgamy syngamy between the 

 and the body enclosed ,.,./,, , J . , 



in a cyst. N, Macro- youngest individuals, products of the rapid 



peristome multiplication of an adult. Conjugation of 

 swarm-spores is by far the commonest type 

 of syngamy in Protozoa, and may be re- 

 garded as the normal type. In this case there is usually complete 

 isogamy, as in Foraminifera (p. 235), sometimes slight anisogamy, 

 as in Radiolaria (p. 254, Fig. 108). 



3. Mixed microgamy and macrogamy that is to say, syngamy 

 between a full-sized adult individual on the one hand and a minute 

 individual, a swarm-spore, on the other hand. This type may be 

 regarded as derived from microgamy by progressive, and finally 

 complete, inhibition of the divisions that produce the swarm-spores 

 in one sex possibly also with an enhanced tendency to such divisions 

 in the other sex. Thus in Arcella, as described in the previous 



nucleus ; P, 



and adoral ciliary spiral. 



After Hickson. 



