ii6 PARAMGECTUM, STYLONYCHIA, OXYTRTCHA LESS. 



process. Soon after this the gametes separate from one 

 another and begin once more to lead an independent 

 existence; the conjugation nucleus of each undergoing 

 a twice repeated process of division, the infusor thus 

 acquiring four small nuclei (F). Two of these enlarge 

 and take on the character of meganuclei (G, Mg. nu\ the 

 other two remaining unaltered and having the character of 

 micronuclei (Mi. nu). Thus shortly after the completion 

 of conjugation each individual contains two mega- and 

 two micronuclei all derived from the conjugation-nucleus. 

 Ordinary transverse fission now takes place, as described 

 in the preceding paragraph, each of the two daughter cells 

 having one mega- and one micronucleus, and thus the 

 normal form of the species is re-acquired. 



It will be noticed that, in the present instance, conjuga- 

 tion is not a process of multiplication : it has been 

 ascertained that during the time two infusors are conju- 

 gating each might have produced several thousand offspring 

 by continuing to undergo fission at the usual rate. The 

 importance of the process lies in the exchange of nuclear 

 material between the two conjugating individuals : without 

 such exchange these organisms have been shown to undergo 

 a gradual process of senile decay characterized by diminution 

 in size and degeneration in structure. 



Another ciliated infusor common in stagnant water and 

 organic infusions is Stylonychia mytilus, an animalcule vary- 

 ing from y^rnm. to |mm. 



Like Paramcecium it is often to be seen swimming rapidly 

 in the fluid, but unlike that genus it frequently creeps about, 

 almost like a wood-louse or a caterpillar, on the surface 

 of the plants or other solid objects among which it lives. 

 In correspondence with this, instead of being nearly 



