354 



I. Platyelminthes. ^ 



Trematoda (Distoma, Monostomuui). 

 Cestoda (Tsenia, Bothriocephalus). 

 Nemertina (Nemertes). 



Nematodes (Strongylus, Ascaris). 

 Gordiucea (Gordius, Mermis). 



III. Ch^etogn.vthi (Sagitta). 



IV. Acanthocephali (Echinorhynchus) . 



V. Rotatoria (Brachionus, Rotifer). 



VI. Polyzoa (Alcyonella, Flustra, Lepralia). 



VII. Enteropneusti (Balanoglossus). 



VIII. Tunicata (Appendicularia, Ascidia, Pyrosoma, Doliolum, Salpa). 



IX. Gephyrea (Sipunculus). 



X. Brachiopoda (Lingula, Terebratulina). 



XI. Asnulata (Himdo, Lumbricus, Nereis, Serpula). 



I. PLATYELMINTHES (Flat Worms, Flukes and Tape Worms). 

 These are flat-bodied ciliated worms without lateral appendages, 

 usually with hooks or suckers. They are usually hermaphroditic. 



Development of the Turbellaria. These lowest of worms, in 

 which there is no true stomach and intestines, but a simple short 

 blind digestive sac leading from the mouth and 

 pharynx, are known to multiply by fission, the 

 HHH| body dividing into two. They also possess ovaries 

 and male glands, and reproduce from eggs. We 

 !■ are not acquainted with the life-history of the 

 |HHH Rhabdocoelous forms, such as Vortex, Prostomum, 

 ■BHH etc., except that we know that they produce eggs 

 ^^Hj^H and spermatic particles. In Prostomum, an orbic- 

 ular form, the yolk cells are formed in a gland 



IHBh ( viteii °s ene ) distinct fr ° m the true ° var >' ° r germ * 



^^HSffl forming gland (germogene). As an example o 

 ■ reproduction by fission may be cited the singular 

 ^^^^^^ Catena quaterna Schmarda, which occurs in fresh 



a ena qua ema. ^ ^ ^ ^ ^ m ^ e . 



sents two individuals in partial division, and a chain of four ind 

 viduals, natural size. This form reminds us of the 



