458 THE PROTOZOA 



When a ciliate for example, a Paramecium is captured by the tentacle,, 

 its protoplasm streams down the tentacle to form a mass in the endoplasm 

 of the acinetan. Before the process of suction is complete the mass breaks; 

 up into smaller masses, and these again into still smaller ones, which are 

 carried away by the cyclosis of the endoplasm, and other masses of snvill 

 size continue to be formed at the base of the tentacle. Round each of thcso 

 food-masses a fluid vacuole is formed, in which the ingested protoplasm is 

 for the most part dissolved, becoming reduced to a few granulations. The- 

 vacuole then gives off fluid and diminishes in size, and the contents are con- 

 centrated to form a refractile body. Three kinds of such retractile bodies are 

 formed : so-called "colourless bodies" which stain feebly with nuclear stains, 

 and are derived from the protoplasm of the prey ; " tinctin-bodies," staining 

 deeply, and originating, as described by Martin, from the chromatin of the- 

 prey ; and others, found in some acinetans, derived from the chlorophyll of 

 green ciliates and algal spores devoured by the animal. If a Tocoplirya be 

 starved, the ref ringent bodies are slowly absorbed, and the protoplasm becomes 

 quite clear (Filipjev). Hence the refringent bodies that arise from the diges- 

 tive vacuoles represent reserve-material ; there appears to be no defaecation 

 of indigestible residues. 



The nature and origin of the tentacles of acinetans have been much dis- 

 cussed, and some authors have sought to derive them from cirri or cilia. 

 Schuberg (44) points out, however, that the structure of the tentacles is quite 

 the opposite of that of the cilia ; in a cilium the axial portion is of firm con- 

 sistence, the superficial layer is fluid, while in a tentacle the axis is fluid and 

 the superficial sheath is of firm texture. Collin (877) considers that the pre- 

 hensile tentacles are modifications or adaptations of a pseuclopodium-like 

 process ; on the other hand, he regards the suctorial tentacles as organs of 

 quite a different kind, more like the cytostome of a ciliate than anything 

 else ; they may be considered each as a cytostome which has grown out from 

 the body on a slender process or stalk (compare also Hickson, 826). 



In correlation with their sedentary habits, the organization of the 

 Acinetaria is greatly simplified as compared with the Ciliata, and 

 the remarkable structural and functional differentiation of the 

 ectoplasm seen in the Ciliata is wanting altogether in Acinetaria, 

 in which the ectoplasm is relatively a feebly-developed layer. Con- 

 tractile vacuoles are usually present, one or more in number. As 

 in Ciliata, the macronucleus exhibits a great variety of forms. One 

 of the most remarkable is seen in the colonial form Dendrosoma, 

 where the macronucleus is branched to the same degree as the 

 colony, throughout which it extends continuously. 



The methods of reproduction are more varied, and exhibit a 

 greater specialization, in the Acinetaria than in the Ciliata. Simple 

 binary fission in the adult condition is rare in acinetans. Collin (881 ) , 

 however, has observed division into two or four within a cyst in 

 Podophrya fixa. The fission usually takes the form of bud-forma- 

 tion. The buds may be formed either on the exterior of the body 

 or in the interior in special brood-cavities, and they may be pro- 

 duced in either case singly and successively or in batches or relays 

 of several at a time. The bud is usually a simple outgrowth of the 

 cytoplasm containing a prolongation budded off from the macro- 

 nucleus, and one of the daughter-nuclei derived from a division of 

 the micronucleus. At first a simple cell without structural differ- 



