PLATYHELMINTHES 73 



Type of Group — Planaria. Anatomy of P. maculata. — The body- 

 wall consists of the ciliated epidermis basement membrane, circular 

 muscles, external longitudinal muscles, internal longitudinal mus- 

 cles, outside of the connective or packing tissue, called parenchyma. 



Digestive System. — The mouth is situated at the end of a pro- 

 trusible proboscis or pharynx, which is midventral. The mouth 

 leads into a central tube which may be axial as in the Rhabdocoela, 

 or branch, one running towards the head, and two, postero-laterally, 

 towards the tail. Digestion is both intercellular and intracellular. 

 Irregular columnar cells and goblet cells line the digestive cavity. 

 The goblet cells secrete an enzyme, probably used entirely in the 

 digestion oi fat. Intracellular digestion begins when the columnar 

 cells push out pseudopodia which seize and ingest food particles, 

 which later appear in vacuoles. There is no anal opening and any 

 undigested food must be discharged from the mouth. 



There are no well-developed circulatory or respiratory systems, 

 as the branched digestive tract distributes the food in the form of 

 lymph. 



Excretory System. — The water vessels of the excretory system 

 run through all parts of the body. They consist of two main 

 longitudinal trunks running on the right and left sides of the body 

 and opening externally on the dorsal surface by means of several 

 minute pores; connected in front by a transverse vessel. From 

 each main trunk come numerous branches which give off in turn a 

 system of fine vessels which terminate in flame cells, which are cells 

 with cilia directed down the tube. Some zoologists think that they 

 may also be respiratory in function. 



Reproductive System. — The reproductive system is hermaphroditic 

 (monoecious). The male part of the apparatus consists of the 

 testes., vasa deferentia and cirrus or penis. The testes are numerous, 

 rounded structures situated near the right and left borders. Two 

 ducts, the vasa deferentia, run backwards from the neighborhood 

 of the testes and unite in the middle line posteriorly. The median 

 duct thus formed passes into the protrusible cirrus which opens in 

 the genital cloaca. At the base of the penis the seminal vesicles 

 empty, while the ducts of the prostate glands also empty into the 

 canal. The female reproductive organs consist of the ovaries, 

 oviducts, vitelline glands {yolk glands) and the uterus, a muscular sac. 

 Fertilization takes place in the uterus and the eggs develop in cocoons 

 that are passed along the oviducts from the animal's body, producing 



