RUDIMENTARY ORGANS OF ANIMALS 



123 



pn 



i.e. their organs of locomotion. In some colonies 

 of Hydroi'ds, polymorphism has made such advances 

 that there are tactile individuals of which the 

 digestive tube lacks both mouth and tentacles, and 

 other purely defensive individuals of which the 

 internal organs are almost all in a state of atrophy. 



Opinions differ regarding 

 the complicated question of 

 the structure of the Siphon - 

 ophora. The organism (fig. 

 52) may be regarded as a 

 simple medusa of which 

 the different appendages 

 the pneumatophore (pn.), 

 the swimming bells (cl.), 

 the siphons (s.), the shield 

 (&.), the tentacle (.), the 

 palp (pa.), the gonophores 

 (go.), etc. constitute the 

 organs, or as a colony each 

 part of which is represented 

 by an individual polypoid 

 adapted to fulfil a special 

 function. Whatever theory 

 is accepted, it is clear 

 that a whole series of parts of the creature must be 

 regarded as organs in a condition of degeneration. 



We accept the second of these theories, 1 and 



1 Haeckel, System der Medusen : Jena, 1880-J881. A. Lang, 

 Trait^ d'anatomie comparte, 



FIG 52 _ Diagram of the structuve 

 n. 



<* *JS& 



trition. 



