270 PLATHELMINTHES. 



region usually bears two or more simple eyes, and in a few a single 

 otocyst. 



In many Turbellaria 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 project 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 

 plants. 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. 



-En 



FIG. 230. Larva of Stylochus pilidium. (From Korschelt-Heider, after Gotte.) D, 

 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 reproduction 

 occurs. The Microstomidge and some Planarice 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). The Turbellaria 

 possess the power, to a marked degree, of reproducing lost parts, 

 which makes them favorites for regeneration experiments. 



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

 organs. The pharynx connects with an entodermal syncitium, a proto- 

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

 toplasm of a protozoan, the food is digested. This entoderm is hardly 



