14 BRITISH HYDROID ZOOPHYTES. 



power of reproduction by means of ova.* 

 This order of reproduction is usually described 

 as " Alternation of generation," and this is the 

 earliest instance of its occurrence in the animal 

 kingdom. It is very important to realize these 

 steps, more especially as they are to a great 

 extent obscured in many instances. We will 

 therefore enumerate them thus : 



The "Alimentary" polypite. 1. Ali- 

 mentary Polypite. The ordinary colonial 

 polypite, whose only duty is to obtain and 

 assimilate food for itself and the colony, but 

 which takes no part in the work of propaga- 

 tion. 



The "Select" polypite. U.f "Select" 

 Polypite. Certain of the above, which, 

 for reasons stated in the foot-note, we 



*It is extremely interesting to note the parallelism with 

 this order in the plant world. For example: Amongst the 

 Ferns (Cryptogams), if one of the spores found on the back of a 

 frond be sown, the result will not be a fern, but a very small 

 and simple plant a leafy expansion, called a prothalium. It is 

 the function of this little plant to produce the male and female 

 elements ; and so soon as fertilization has taken place it dies 

 leaving the embryos (" oo-spheres "; to develop into proper 

 ferns. 



tThe "Gonoblast" idea of Huxley and the "fertile 

 polypite" of Hincks. Some apology seems necessary for 

 presuming to suggest a more suitable term for these Buds, in 



