114 



THE INVERTEBRATA 



Order CHONOTRICHA 



Ciliata, permanently sessile by the posterior end upon the bodies of 

 Crustacea; with the peristome represented by a spiral funnel at the 

 anterior end, coiled clockwise, ciliated inside, and leading to the 

 mouth; and the rest of the body naked. 



A small but very interesting group which shares with the Prociliata 

 two characteristics not found elsewhere in the class, namely (i) that 

 their nuclei are of one kind only and at mitosis form two sets of 

 chromosomes (see p. 26), (2) that they form numerous gametes, 



mi.-if--^ 



Fig. 94. Fig. 95. 



Fig. 94. Spirochona gemmipara, x 520. ach. achromatic part of nucleus 

 (centrosphere) ; chr. chromatin ; mi. micronucleus (which divides within mega- 

 nucleus, where it appears when division is impending). 

 Fig. 95. A diagram of the formation of an internal bud by one of the Suctoria. 



which unite in the same way as those of members of the other classes 

 of the phylum. In the Chonotricha the reproduction, both sexual and 

 asexual, is carried out by buds. The nucleus contains a large achro- 

 matic mass which acts as a division centre. 



Spirochona (Fig. 94). Shaped like a slender vase. On the gills of 

 Gammarus, etc., in fresh and marine waters. 



Subclass SUCTORIA 



Ciliophora of which all but a few primitive forms lose their cilia in 

 the adult; and which possess one or more suctorial tentacles. 



A few members of the group are free ; a few are endoparasitic ; most 



