XX11 



INTRODUCTION. 



flower-bud of the plant, they have their many forms and 

 even colours. If we examine their structure we find that 

 the apparent differences amongst them are numerous and 

 striking ; but a closer investigation shows us that, amidst 

 all the deviations, a community of plan may be traced. 



The sexual bud consists (almost universally) of an outer 

 investment (the ectotheca), which serves as a protective 

 case, and a contained zooid, which may be male or 

 female, and which originates sooner or later the gene- 

 rative elements. The two sexes are sometimes borne on 

 the same colony, but more commonly the zoophyte is 

 dioecious. The cases, however, are much less rare than 

 had been supposed, in which both the male and female are 

 mingled on the same shoots. The Hydra is sometimes 

 monoecious and sometimes dioecious, the true representative 

 of its Order in this as in so many other points. 



The sexual zooids are either fixed or free. They either 

 continue attached and mature and discharge their con- 

 tents in situ (Woodcuts, figs. viii. and ix. ), or at a certain 



Fig. viii. 



Fig. ix. 



VIII. The gonopliore of Clava. a. The spadix, communicating with the 

 ccenosarc. b. The endoderm of the gonozooid. c. The ectoderm of the same. 

 (I d. The ectotheca, enclosing the gonozooid. a'. Ovum. The gonozooid. 

 n, b, c, is the equivalent of the manubrium. IX. Gonophore of Aglaophcnia 



