i8o MINUTE MARVELS OF NATURE 



the toilet of one host, he leaves his place for 

 another with a more favourable field for his 

 labours. 



Fish have other organisms which take up their 

 abodes temporarily on their skin surface ; for on 

 my table while writing I have in a small tube of 

 spirit a creature that I have just obtained from a 

 roach. It is worm-like, about an inch in length, 

 tapering slightly to one end. The broader end is 

 terminated by a large sucker, and at the tapering- 

 end this is repeated on a smaller scale. This 

 lively creature, with a sucker at its head and tail, 

 was adhering by means of one of these suckers to 

 the skin of the roach. It can detach itself at will, 

 and, like our last subject, pass from one fish to 

 another. Thus it is evident that fishes have to 

 play host to various visitors at times. 



While the study of these creatures which infest 

 others may not at first present itself as a very 

 agreeable subject, yet as we have seen, it possesses 

 some exceedingly interesting features. As there 

 are probably no animals that exist without their 

 parasites, the study of these naturally provides a 

 prodigious field for scientific work. There are 

 many creatures of this class which are quite 

 familiar to scientists, yet of whose life history 

 little or nothing is known. 



The difficulties in the way of the study of these 



