MEANS OF TAKING IN FOOD, 



47 



secure food, to divide it, and to transmit it to the stomaoli after 

 being well comminuted ; while man also requires the assistance 

 of the cook in the pi-eparation of his food. Now although, 

 from a physiological point of view, these auxiliary organs are of 

 less importance than the digesting intestinal canal, they are of 

 the highest interest for us, inasmuch as they involve an endlessly 

 varied series of links between animals and the conditions under 



Fig. 12t'—Sacctilhm caixini, with the tuft of clinging roots which it inserts into the body 

 of its host ; 6, its larva (Nauplius) ; c, Thompsania globosa (Kossmann) ; d, its larva, 

 Cypris stage. 



which they live, in addition to those which arise from the mere 

 quality and quantity of the nourishment required. 



The peculiar mode of taking up nourishment exhibited by 

 various Parasites must also be shortly described. Asa rule, 

 almost without exception, the larvse of parasites swim or move 

 freely about in water (leading a very unfitly termed active life). 

 During this stage of free locomotion the larvee are usually high 

 in the scale of structure. The larva of the parasitical Copepoda 

 or Cirrhipedia (for instance, of a Sacculina, fig. 12) is known 



