34 



DEGENERA TION. 



comparatively simple bodies ; and this is true of 

 their internal structure as well as of their external 

 appearance. The most utterly reduced of these para- 

 sites is the curious Sacculina (Fig. 7) which infests 



Fig. 7. — Adult Sacculina (female). 



Hermit-crabs, and is a mere sac filled with eggs, and 

 absorbing nourishment from the juices of its host by 

 root-like processes. 



Lernseocera again, which in the adult condition 

 is found attached to the gills of fishes, has lost the 

 well-developed legs of its Nauplius childhood and 

 become an elongated worm-like creature (Fig. 8), 

 fitted only to suck in nourishment and carry 

 eggs. 



Amongst these Nauplii — all belonging to the great 



