Reproductive System of Sertularian Zoophytes. 389 



of the internodes of that rib or axis. If these bodies were only- 

 ordinary cells changed, they would take the place of ordinary cells, 

 and if unilateral on the axis, spring opposite the corresponding 

 cells, but they do not : they arise unilaterally between the pairs 

 of cells in the manner of branches. 



From the foregoing considerations, the theory of the nature of 

 the ovigerous vesicle in the Sertularian Zoophytes may be stated 

 thus : — 



The vesicle is formed from a branch or pinna through an arrest 

 of individual development by a shortening of the spiral axis, and 

 by a transformation of the stomachs (individuals) into an ovige- 

 rous placenta, the dermato- skeletons (or cells) uniting to form 

 a protecting capsule or germen, — which metamorphosis is exactly- 

 comparable with that which occurs in the reproductive organs of 

 flowering plants, in which the floral bud (normally a branch 

 clothed with spirally arranged leaves) is constituted through the 

 contraction of the axis and the whorling of the (individual) ap- 

 pendages borne on that axis, and by their transformation into 

 the several parts of the flower (reproductive organisms) . 



Whether the transformation in the case of the Sertulariada 

 takes place ab initio, or after the individuals have performed 

 for a time their normal function of stomachs, can only be 

 answered by observations on the development of the living zoo- 

 phyte. 



Among the most convincing facts favouring the theory of vege- 

 table morphology are monstrosities which every now and then 

 occur, in which we find the floral axis and its appendages par- 

 tially transformed into a folial axis and appendages. 



Now if the views I have advanced be true, we should expect 

 to find similar cases of monstrosity among Sertularian Zoophytes. 

 I find on searching the records of zoophytology two figures which 

 appear to represent monsters of the kind required. 



The first is a figure of Plumularia cristata in Dr. Johnston's 

 ' History of British Zoophytes/ pi. 19. f. 2, where a branch is re- 

 presented as partially transformed into an ovigerous vesicle, whilst 

 the polypes of the lower or basal extremity retain their normal 

 character of nutritive individuals. 



The second is a remarkable zoophyte described and figured by 

 Dr. Fleming in the ' Wernerian Transactions/ vol. v. pi. 9, under 

 the name of Plumularia bullata, in which branches bearing regu- 

 lar cells seem to spring out of vesicles, and to be changed in some 

 instances into vesicles again. 



The consideration of this subject naturally leads us to inquire 

 how far it influences systematic zoophytology, and how far we 

 should consider the form of the vesicle as of generic or specific 

 value. I am inclined to regard its importance as generic. If so, a 



