viii ROTIFERA 103 



cated in internal structure, for tbey have a body-cavity 

 (coelom) distinct from the alimentary canal, and also excretory, 

 reproductive, and nervous systems, the brain being relatively 

 large, though the sense organs are very simple. 



Most of them live freely in fresh water, though a few 

 are marine, and most of them live free independent lives, 

 though a few are parasitic, as e.g. Notommata Werneckii, which 

 is not infrequently met with inside the jSlaments of the fresh- 

 water Alga, Vaucheria, where it forms gall-like swellings. 



In the summer these Eotifers usually lay parthenogenetic 

 eggs of two sizes, the larger eggs giving rise to females and 

 the smaller to males. Before the winter, they also lay thick- 

 shelled winter resting eggs, which develop in the following 

 spring. These eggs have probably been fertilised. The 

 adult active individuals have but short lives. In the case of 

 Hydatina, which has been carefully investigated, the longest 

 life seems to last not more than thirteen days. 



Classification of the TVorms mentioned in Chapter VIII. 



Phylum VI. Platyhelminthes (Flat-worms). 

 Class I. Turbellaria (Whirl-worms). 



Order 1. Polycladida (marine forms with many lateral 

 branches to stomach). 

 Leptoplana. 

 Order 2. Tricladida (those with only three main branches to 

 the stomach). 

 Planaria. 

 Order 3. Rhabdocoelida (those with a straight, rod - like 

 alimentary canal). 

 Mesostoma. 

 Class II. Thematoda (Liver-flukes). 



DistoTnum hepaticum. 

 Class III. Cestoda (Tape-worms). 



Taenia solium. 

 Class IV. Nemertinea (Ribbon-worms). 

 Lineus marinus, the Sea-snake. 

 Phylum VII. Nematoda (Kound or Thread-worms). 

 Ascaris lumbricoides. 

 Trichina spiralis. 

 Phylum VIII. Polyzoa (Sea-mats or Corallines). 



Marine forms. — Fliistra, Flustrella, Membranipora, Bugnla. 

 Fresh-water forms. — Cristatella, Lophopns, Plnmatella. 



