INTRODUCTION. xxi. 



endowed with the function of sexual 

 reproduction, but certain members produce 

 Special Bads which are so endowed, the 

 bearers of these buds becoming considerably 

 modified in consequence. They are devoid of 

 mouth or tentacles, and so do not concern 

 themselves with procuring food. They are 

 termed Blastostyles. The Special Reproductory 

 Buds, in the lower forms of Hydroids, are 

 liberated as Jelly-fishes, and disperse with 

 their contained ova, to other parts. In the 

 higher forms of Hydroids, these Reproductory 

 Buds remain attached, setting free the ova in 

 situ. Before liberation, the ovum undergoes 

 segmentation, and produces, by a process of 

 inversion, a central cavity — the future 

 stomach. The embryo is termed a Planule, 

 and is provided with cilia, by means of which 

 it swims away, shortly attaches itself to some 

 object, forms rootlets by the splitting up of 

 the expanded base of attachment, and also 

 develops a mouth and tentacles ; it then 

 becomes an ordinary Polypite, which, as 

 growth proceeds, buds and forms a new 

 colony. 



P. J. R. 



