The protonephridial excretory system consists of a network of fine tubes 

 with branches terminating in flame cells and with many pores on the 

 surface of the body. 



Muscular fibers are found in several layers underlying the epidermis 

 (integumental muscles), individual fibers traversing the parenchyma in 

 various directions, and variously arranged fibers in the pharynx, the 

 adhesive organ when present, and in parts of the reproductive system. 



No separate circulatory system is developed, its functions being taken 

 over by the gastrovascular cavity and the system of interstitial spaces 

 of the parenchyma. 



The parenchyma contains the cell bodies of many unicellular glands, the 

 ducts of which open through the epidermis to the outside, through the 

 surface of the adhesive organ, the tip of the pharynx, and various parts 

 of the reproductive organs. 



The taxonomically most important structures are those of the reproductive 

 system. All freshwater planarians are hermaphroditic, both male and 

 female genital organs developing in the same individual (Fig. 3). The 

 paired ovaries or germaries (ov) lie in the anterior portion of the 

 body adjacent to the ventral nerve cord. From each ovary originates a 

 canal, the oviduct or ovovitelline duct (od) which proceeds posteriorly 

 along the dorsal side of the nerve cord. At the boundary between the 

 ovary and the oviduct is a small enlargement of the canal, the seminal 

 receptacle. Many vitellaria or yolk glands (vi) branch out from the 

 oviduct, consisting of large eosinophilic cells with yolk inclusions. 

 Cell masses, representing a transition between oogonia and yolk cells, 

 may be attached to the ovaries, forming the so-called parovaria. 



The male gonads are numerous testicular follicles (t) located on either 

 side in a zone extending from behind the ovaries to the level of the 

 pharynx, the mouth, or almost to the posterior end (exceptionally, the 

 testes may fuse into one elongated organ on either side) . Each testis 

 is connected to the sperm duct or vas deferens (vd) by a thin canal, the 

 vas efferens. The sperm ducts run posteriorly parallel to the nerve 

 cords. In the region of the pharynx they usually widen, forming twisted 

 enlargements filled with sperm, the false seminal vesicles or spermi- 

 ductal vesicles (sv) . 



Behind the pharynx is the copulatory apparatus or complex consisting of 

 the terminal portions of the gonoducts and various accessory structures. 

 The genital aperture (gp) leads into a cavity, the genital atrium or 

 antrum, which may be subdivided into several parts separated by stric- 

 tures: a male atrium (am) enclosing the penial papilla, a female atrium 

 receiving the openings of parts of the female complex, and a common 

 atrium (ac) which connects with the gonopore. The nomenclature of the 

 atria is frequently inconsistent, as the mouth of the oviduct may be in 

 the posterior part of the "male" atrium. 



