84 



COMPAEATIVE ANATOMY. 



cases there is really one and the same pliEenomenon. Any place in 

 the protoplasm can act as a digestive cavity by enveloping 

 and absorbing nutritive matter, and at any neighbouring part 

 of the smiace the undigested substances can be again expelled. 

 Even in Actinosphasrium solid food can be taken into the body ; but 

 in it the pseudopodia are not the direct agents, for they draw the 

 prey to the body, and cause it to pass into the yielding parenchyma 



of the cortical layer at some suitable 

 point (Fig. 27) ; thence it passes to 

 the central substance of the body. 

 In comparison with other forms Acti- 

 nosph^rium is characterised by taking 

 its food directly into the more differ- 

 entiated pai'ts of the body, and not 

 surrounding it by the amorphous 

 protoplasm of the pseudopodia. 



In the Infusoria the arrangement 

 is more definite. They take in food 

 in two different ways. In the Suc- 

 toria (Acinetinte) there is no mouth ; 

 the radiate pseudopodia-like processes 

 pass through the envelope of the 

 iDody, and act as suckers (Fig. 30). 

 They attach themselves by their 

 sucker-like enlargements to the prey 

 which has come within their reach 

 (which consists of other Infusoria, etc.), and cause it to flow, as 

 through a tube, into their body, where it fills the parenchyma in 

 the form of drops. The presence of similar processes in the 

 embryos of other Infusoria shows that this mode of nutrition is 

 a very common one. A higher gi^ade is represented in the other 

 forms J in the Ciliata there are not only definitely organised parts 

 for the reception of food, but also definite parts for the ejection 

 of what is useless. An enteric tube is, however, wanting in all 

 of them, and these differentiations are limited to the cortical layer 

 of the body, so that the food passes beneath it into soft paren- 

 chyma, i.e. into the undifferentiated protoplasmic part of the body, 

 in which there are no passages with special walls. Temporary 

 spaces, which act as digestive cavities for the spherical food masses, 

 are formed in it ; these cavities are not permanent ones, as may be 

 seen from their frequent disappearance when the protoplasm is in 

 movement. In this point, therefore, they resemble the Ehizopoda ; 

 for a part of the digestive apparatus, that is those parts in which 

 the food is digested, have no organological differentiation. 



When the Ciliata have a mouth, it is either in the form of a 

 simple cleft, which is in many cases only apparent when food is 

 taken in ; or it is not directly on the surface of the body, but at the 

 bottom of a depression (vestibule), the form of which is very vai-ied, 

 and which at times contains the orifice of egestion also ; the sur- 



Fig. 27. Actinosph03rium. a A 

 morsel wbich has been taken in as 

 food, and just pushed into the soft 

 cortical layer b, by the animal, 

 c Central parenchyma of the body. 

 d Some balls of food in it. e Pseu- 

 doj>odia of the cortical layer. 



