152 



HELMINTIIOZOA. 



Fig. 75. 



(404.) The mouth, in a few species of Planariae, is placed at the 

 anterior extremity of the body, but generally 'it is found to occupy the 

 middle part of 'the ventral surface. Its structure is quite peculiar, and 

 admirably adapted to the exigences of the creature : it consists of a 

 wide, trumpet-shaped proboscis (fig. 75, 3 & 4), which can be protruded 

 at pleasure, and applied to the surface of such larvae or red-blooded 

 worms as may come within reach, so as to suck from them the juices 

 which they contain ; or if the prey be small, such as animalcules and 

 minute Crustacea, they 

 are seized by it and con- 

 veyed into the digestive 

 canals. The internal 

 organs appropriated to 

 nutrition resemble in all 

 essential points those of 

 theDistoma; they consist 

 of a multitude of blind 

 tubes, ramifying in the 

 parenchyma of the body, 

 which, when distended 

 with coloured substances, 

 are sufficiently distinct. 

 The principal trunk (fig. 

 75, l), which communi- 

 cates with the probosci- 

 diform mouth, soon di- 

 vides into three primary 

 branches, one of which 

 runs along the median 

 line towards the anterior 



extremity, whilst the structure of Planaria (after Duges). 1. Ramifications of 

 Other two are directed alimentary canal. 2. Vascular system. 3. Proboscis un- 



backwards towards the 

 tail. From these central 

 canals secondary ones are 

 given off, which permeate all parts of the creature. There is no anal 

 aperture ; so that, of course, the residue of digestion is expelled through 

 the mouth ; but the nature of the process by which defecation is thus 

 effected is curious : the Planaria, slightly bending itself, is seen to pump 

 up through its proboscis a quantity of water, with which all the branches 

 of the alimentary ramifications are filled ; the creature then contracts, 

 and, forcibly ejecting the contained fluid, expels with it all effete or 

 useless matter. 



(405.) In the larger marine species, M. de Quatrefages* recognizes 



* Ann. des Sc. Nat. 1845. 





folded. 4. Represents a Planaria devouring a N"ais, showing 

 the action of the proboscis. 5. Generative system : a, male 

 apparatus; 6, female ditto. 6. Two Planarise in the act of 

 copulation. 



