l8o AQUATIC MICROSCOPY FOR BEGINNERS. 



The two caudal prolongations are movable and flexi- 

 ble. Their chief use seems to be to anchor the 

 animal to the glass slide or cover, or to some object 

 in the water, clinging with their tips, and apparently 

 assisted by a secretion that is supposed to exude from 

 them, this sticky fluid passing from two ovate glands 

 usually visible in the upper or anterior part of each. 



The mouth opens into a strongly muscular oesopha- 

 gus, which itself opens into the intestine, a tapering, 

 tubular passage lined with nucleated cells and passing 

 in almost a straight course along the median line to 

 terminate between the two caudel prolongations. If 

 the observer can get the animal in such a position 

 that he can focus down on the front of the head., he 

 will see that the cavity of the oesophagus is triangular. 

 It is not very diffcult to do this, since the little creat- 

 ures are exceedingly restless; -they are continually 

 turning and writhing about, and lifting the head in 

 various directions. This feature in its structure can 

 often be seen in the animal while still in the egg, for 

 even there, when almost ready to escape, it is exceed- 

 ingly restless. The eggs are not rarely found on the 

 slide, with the young Chsetonotus doubled up and 

 squirming within. 



The eggs by which Chsetonotus is reproduced are 

 formed in an ovary difficult to see unless occupied by 

 an egg, but placed in the median line of the body im- 

 mediately above the intestine. Usually only one egg 

 is formed at a time, but ■ it is not rare to see two or 

 more in various stages of ovarian development. JJpon 

 the absence or presence of an egg in the ovary de- 

 pends, to a great extent, the degree of convexity of 

 the back. The eggs are dropped anywhere in the 

 water, and left to the care of Nature. 



