74 INVERTEBRATE ZOOLOGY. 



well studied in the living animal by compressing it slightly. Cnt from a piece 

 of cardboard a frame the size of the cover-glass and 2-3"'™ wide. Soak it in 

 water and apply it to the center of a slide. Place a living specimen in this 

 with a drop of water, cover and examine. By this means the animal will be 

 slightly flattened and its motions circumscribed. Observe the following — 100''. 



a. Alimentary canal. The mouth is near the centre of the under side and 

 is best seen by placing an animal ventral sideux), although it may be generally 

 made out by focusing through the body. It is circular and may be seen to 

 open and close dxiring the muscular contortions of the animal. The mouth is 

 connected with the main alimentary tract by a cylindrical pharynx, which in 

 a flattened animal may lie unsjanmetrically upon the side. The canal itself 

 is rather opaque, owing to its contents, and may be variously shaped [40]. 



b. Reproductive system. Turbellaria are hermaphroditic and the organs of 

 both sexes are very complicated and often dendritic. Two sets of branching 

 organs may be seen at the sides terminating in finger-like lobes. Of these, 

 the thickest lobes, showing white by reflected light, and visible with the sim- 

 ■ple lens, are the yolk glands. The other set, similar, but more delicate, forms 

 the testes. The uterus, also branched, is very thin walled and almost invisi- 

 ble, but is generally easily located by the large conspicuous eggs which it con- 

 tains. If these are numerous, they will be seen to be arranged in rows which 

 mark the disposal of the uterine tubules. 



c. Nenioii.s system. The pigment eyes may be seen to rest upon an opaque 

 mass from which pass four branches, two anteriorly and two posteriorly. 

 The main mass forms the brain, and the branches are the four principal nerve 

 cords. The anterior cords may be followed into the very extensile anterior 

 end, where they resolve themselves into a brush -like mass of minute nerves, 

 which render this extremity a very sensitive tactile organ. The posterior 

 cords run down the sides of the body and divide into minute nerves. There 

 is often a commissure just posterior to the pharynx connecting the two poste- 

 rior cords. 



d. Nephridial system. This is an important system, but hard to make out 

 in a living specimen. Four branching tubes, two anterior and two posterior, 

 collect the liquid excreta from the body parenchyma. On each side the ante- 

 rior and posterior tube join and form thus two lateral ducts which run into 

 the pharynx near the mouth. 



e. Cilia. These are visible only at the edge, but it mxist be c(mcluded that 

 they cover the entire surface, from the fact that they are visible along the 

 entire edge and at every edge that may be formed by chance foldings and 



