CONJUGATION 113 



Conjugation also occurs, usually after multiplication by 

 fission has gone on for some time, but the details and the 

 results of the process are very different from what are found 

 to obtain in Heteromita (p. 62). Two Paramcecia come 

 into contact by their ventral faces (Fig. 22, A) the nuclei and 

 paranuclei break up (B N) and are afterwards reconstituted 

 (o, P) : at a certain stage in the process the two conjugating 

 individuals or gametes separate from one another (H, i), the 

 union being thus a temporary one, and not followed by the 

 production of a zygote or by spore-formation. It is certain, 

 however, that conjugation has a beneficial effect, which in 

 all probability is due to an exchange of nuclear material. 

 The process is exactly comparable to that which occurs in 

 the sexual reproduction of multicellular animals (Lesson 

 XXIV.). 



The conjugation of the ciliate Infusoria presents so many peculiarities 

 and is so difficult of observation, that very various accounts of it have 

 been given by skilled observers. The following abstract of Gruber's 

 elaborate researches on the process as it occurs in Paramoecium aurelia 

 may not be out of place, since the student may at any time meet with 

 specimens in conjugation exhibiting one or other of the complicated 

 phases shown in Fig. 22. 



Two individuals become applied by their ventral faces (Fig. 22, A) 

 the paranucleus of each (/) separates from the nucleus (n}, and, after 

 forming the spindle characteristic of a dividing nucleus (B, /), divides 

 into two (c, /\ p 1 }. One of the products of division (p l ) in each 

 gamete approaches the ventral face and becomes flattened out as it were 

 against the cuticle (D, p 1 } : in this way two paranuclei, one from each 

 gamete, are brought into intimate relations with one another, and in all 

 probability an exchange of nuclear material takes place between them, 

 although this has not been actually proved. Next, these two paranuclei 

 take on the form of rounded homogeneous bodies and retreat towards the 

 interior of the Paramoecium (E). The same process is there gone 

 through with the second pair of paranuclei (F, p-), so that foui homo- 

 geneous bodies are produced, two in each gamete (G). Each of these 

 takes on the spindle form (H), and divides, and at this phase the two 



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