SOME AQUATIC WORMS, ETC. 169 



or prickles, or with both scales and spines at the same 

 time. In the latter kinds the scales cover the back and 

 sides, and the spines spring from these appendages, arch- 

 ing back towards the forked tail. And in all cases these 

 little scales are imbricated, or overlapping like the shin- 

 gles on a roof, only they have the curious habit of lap- 

 ping in what seems to be the wrong way, that is, their 

 free margins point towards the animal's head, or in a 

 direction just opposite to that of the scales on a fish. 

 They are usually minute, and require high powers to 

 see them properly. 



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 wa- 

 ter, clinging with the tips, and apparently assisted by 

 a secretion that is supposed to exude from them, this 

 sticky fluid passing from two ovate glands usually visi- 

 ble in the upper or anterior part of each. 



The mouth opens into a very muscular oesophagus, 

 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, terminating be- 

 tween the two caudal 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 cav- 

 ity of the oesophagus is triangular. It is not very diffi- 

 cult to do this, since the little creatures are exceeding- 

 ly restless; they are continually turning and writhing 

 about, and lifting the head in various directions. It can 



