RUDIMENTARY ORGANS OF ANIMALS 129 



and permanent in some other Nematodes. In 

 Ecliinorliynchus, for instance, the digestive tube 

 is absent, and nourishment is obtained by means 

 of osmotic soaking through the body walls. 



The Annelids comprise the annulated sea-worms 

 and forms like the common earth-worm (Lumbricus 

 terricola). In these creatures we will take, first, 

 the development of the eyes. In Oligochcetes, which 

 for the most part live in soil or mud, the organs of 

 sight are greatly reduced. The Naidomorphce alone 

 have eyes. The Archiannelida Histrior (a para- 

 site), for instance possess eyes when young, but 

 in the adult state the eyes have greatly degener- 

 ated. As a rule, the eyes of the Polychcetes are 

 well developed, and in some of them quite re- 

 markably so. In species, however, which do not 

 move about much, the eyes are merely represented 

 by small pigmented spots. 



We may mention, too, the Gfephyreans, without 

 pledging ourselves as to their exact relationship. 

 Bonellia viridis, the history of which is well known 

 and of great interest, belongs to this group. The 

 male Bonellia lives as a parasite on the proboscis, or 

 in the gullet or the nephridium of the female. It 

 is flat and small, and has neither mouth, arms, nor 

 circulatory system. All the organs remain as in 

 the larval condition, with the exception of the 

 genital organs, which are fully developed. 



Bonellia and Dinophilus, a rotifer, of which the 

 male is degenerate, exhibit a progressive degenera- 



I 



