142 MANUAL OF ELEMENTARY ZOOLOGY 



lying in the region where the endoplasm of the conjugants 

 became continuous. One half of each micronucleus passes 

 into the larger conjugant, where the two fuse as male and 

 female pronuclei. The other half of each passes into the 

 smaller conjugant, but these halves, instead of fusing, 

 degenerate and disappear. The endoplasm of the small 

 exconjugant is now drawn into the larger, the ectoplasm 

 shrivelling up and falling off. It will be seen that the 

 conjugation of Vorticella takes place in the same way as 

 that of Paramecium, but that one of the two exconjugants 

 perishes and is partly absorbed by the other. 1 



Carchesium is a small freshwater animal whose body 

 consists of a number of members, each of which 

 has the structure of a whole Vorticella. It 

 arises from a Vorticella-like body, by divisions like those 

 which take place in the ordinary reproduction of Vorticella, 

 save that the division passes some way down the stem and 

 then stops, leaving the bells joined by their stalks. Thus 

 the body is increased by the addition of new members 

 which repeat the structure of the old. In that it increases 

 the number of energids in the body, this process resembles 

 cell formation, but the two cases differ in that the new 

 energids of Carchesium all repeat the whole structure of the 

 first and inherit all its powers, whereas a cell is a portion 

 of the body with peculiar characters and restricted powers. 

 The whole body of a Carchesium is said to be a colony, and 

 its members are zooids. Reproduction is brought about by 

 the complete fission from the body of certain zooids, which 

 thus become asexually produced young or buds. When it 

 has broken off and settled down as an independent indi- 

 vidual each of these becomes by division a new colony. 

 Conjugation like that of Vorticella also takes place. 



The detailed study which we have made of Paramecium 



and Vorticella has shown to what an extent 



organisation can be carried without the division 



of the body into cells. Ranging in grade of organisation 



1 The student should beware of comparing the smaller conjugant of 

 Vorticella with a spermatozoon and the larger with an ovum. Ova 

 and spermatozoa are gametes of unlike kinds. The conjugants of 

 Vorticella are unlike, hermaphrodite parents, each of which forms two 

 unlike gametes. 



