MARINE WORMS 



175 



and above that required for the sustenance of their simple bodies is 

 utilised in the reproduction of the species ; consequently we find, 

 as a rule, the reproductive organs well represented, and the species 

 concerned very prolific. 



It is an interesting fact, too, that these parasites, in their 

 earliest stage, possess organs which are present in the higher 

 worms, but which degenerate 

 as they approach the adult 

 form , thus indicating that they 

 have descended from more 

 respectable members of the 

 animal world, and that the 

 low physical development 

 which they ultimately attain 

 is the natural result of their 

 base mode of living. 



The young marine natu- 

 ralist, working on our coasts, 

 will not be brought into 

 intimate contact with para- 

 sitic worms to any large 

 extent, yet we have said this 

 little on parasitism to show 

 that these degenerate crea- 

 tures are not really devoid 

 of interest, and that they will 

 repay study whenever they 

 are found. They will be 

 more frequently met with 

 during the examination of 

 the animals usually higher 

 types that become then* 

 hosts, and thus they hardly 

 come within the scope of this 

 work. 



The simplest of the worms 

 are those forming the class 

 Turbellaria, so designated on account of the commotion they produce 

 in the water surrounding them by means of the vibratile cilia that 

 fringe their bodies a characteristic that is also expressed by their 

 popular name of Whirl Worms. They are usually small creatures, 



FlG. 116. A TUBBELLAKIAN, 



MAGNIFIED 



a, mouth : 6, cavity of mouth : e, gullet ; d, 

 stomach ; , branches of stomach :/, nerve 

 ganglion ; g to m, reproductive organs. 



