270 



PL A TIIELMINTUES. 



region usually bears two or more simi^le eyes, and in a few a single 

 otocyst. 



In many Tnrbellaria nettle cells, like those of the Ccelenterata, 

 occur in the skin. Much more common are the rhabdites, small 

 rods which arise in epithelial cells which sometimes i^roject like 

 glands into the mesoderm. Those rhabdites occur in the shiny 

 tracks which the animals leave in creeping. 



The hermaphroditic sexual organs (fig. 73) and the excretory 

 system vary considerably in the separate orders and families. The 

 eggs are usually very large and are fastened by a stalk to- water 

 2>lants. Many species form a sort of cocoon, containing a few eggs 

 and numerous yolk cells. In the marine species a free-swimming 

 larva (fig. 230) with lobe-like processes may hatch from the egg. 



FiQ. 230. — Larva of Siylochus pilidium. (From Korschelt-Heider, after Gotte.) I^, 

 enteron ; En, remains of entoderm cells ; .S, oesophagus. 



This larva, by a metamorphosis, is converted into the creeping 

 adult. Not infrequently besides the sexual asexual rejiroduction 

 occurs. The MicrostomidEe and some PlmKirice are capable of 

 transverse division, and, when well nourished, by rapidly repeated 

 divisions will form chains of individuals arranged in a row, separa- 

 tion taking place gradually. For each posterior individual a new 

 brain and a new oesophagus are formed (fig. 58). TheTurbellaria 

 ])ossess the power, to a marked degree, of reproducing lost parts, 

 which makes them favorites for regeneration exjieriments. 



In a few Tiirbelhiria there is a noteworthy condition of the digestive 

 organs. Tlie pharynx connects witli an entodermal syncitium, a proto- 

 plasmic mass, without lumen, containing nuclei in which, as in the pro- 

 to])hism of a protozoan, the food is digested. This entoderm is hardly 



