ANNULOIDA : SCOLECIDA, 



149 



mostly ovoid or elliptical in shape, flattened, and soft-bodied. 

 They are for the most part aquatic in their habits, occurring 

 in fresh water, or on the sea-shore, but occasionally found in 

 moist earth. The integument is abundantly provided with 



Fig. 41. Morphology of Turbellaria. 1. Planaria torva (Muller). m. Mouth; 



?. Nerve-ganglion; e. Eyes ; ov. Ovary; /. Testis ; gn. Genital opening; 

 . Planaria lactea, showing the branched (Dendrocrel) intestine. 3. 

 Microscopic larva of Alaurina, a marine Turbellarian. 4. PiliiUum, the 

 ' pseudembryo ' of a Nemertid. a. The alimentary canal ; 6. Rudiment 

 of the Neinertid. 



vibratile cilia, which subserve locomotion, and it also contains 

 numerous cells which have been compared to the 'cnidse,' or 

 nettle-cells, of the Coelenterata. There is always a considerable 

 portion of the body situated in front of the mouth, constituting 

 the so-called ' prse-oral region,' or ' prostomium ;' and this is 

 often modified into a singular protrusible and retractile organ, 

 called the ' proboscis,' the exact use of which is not known. 

 The mouth opens into a muscular pharynx, which is often 

 evertible ; and the intestine may be either straight or branched, 

 but always terminates caecally behind, and is never provided 

 with an anal aperture. The ' water- vascular system ' commu- 

 nicates with the exterior by two or more contractile apertures. 

 The nervous system consists of two ganglia, situated in front 

 of the mouth, united by a commissure, and giving off filaments 

 in various directions. Pigment-spots, or rudimentary eyes, 

 from two to sixteen in number, are often present, and are 

 always placed in the pree-oral region of the body. The male 

 and female organs are united in the same individual, and the 

 process of reproduction may be either sexual, by means of 

 true ova, or non-sexual, by internal gemmation or transverse 

 fission. 



The Plcmarians have been divided into two sections, as 

 follows : 



Section A. RHABDOCCELA. Intestine straight, not branched. 

 Body elongated, rounded, or oval. 



