RUDIMENTARY ORGANS OF ANIMALS 121 



the Wolffian body plays a considerable part in the 

 formation of the system. This body, the primitive 

 kidney, loses its urinary function at a certain 

 stage of embryonic development, and the permanent 

 kidney which gradually develops alongside, assumes 

 the urinary function. Later on, the Wolffian body 

 assumes new functions, becoming an important part 

 of the genital apparatus. 



In this transformation partial degeneration occurs, 

 resulting in such reduced structures as the epi- 

 didymis, the organ of Rosenmiiller, the vas aberrans, 

 etc. (see fig. 57). 



2. Rudimentary organs in various groups. 



1. Coelenterates. The Coalenterates comprise three 

 great groups. 1 The Anthozoa, of which the coral is 

 a type, the Hydrazoa, which include fresh water 

 Hydra and the common jelly-fish of our seas, and 

 the Ctenophora, of which the chief representative 

 in our seas is Cydippe, a globular transparent animal 

 frequently to be found floating in large numbers on 

 the surface of the water. 



The colonies of Anthozoa are usually composed 

 of individuals all exactly alike. In some species, 

 however, in the Pennatulida? and the Alcyonaria 

 for instance, there is a distinct differentiation 

 amongst the numerous individuals composing the 

 colony. Side by side with sexual individuals 



1 See C. Vogt and Emile Yung, Trait6 d'anatomie compare, vol. i. 



