14 ZOOPHYTES. 



manner as externally, and for like reasons, as the external waters have 

 free admission. 



II. Gemmiparous. — 1. By single buds, developing young, which 

 afterwards become free and independent animals. 



2. By buds, which become developed and remain persistent, — and 

 these may be either lateral or terminal. 



III. By Artificial Sections. 



This mode may depend on the same cause as the general distribu- 

 tion of the budding function, and may be properly an analogous pro- 

 cess, — both depending on the imperfect character of the nervous 

 system, or its absence. 



These modes of reproduction, as they are presented by the diffe- 

 rent tribes of zoophytes, will be farther explained in the following 

 pages. 



8. Compound Zoophytes. It has been stated that zoophytes are 

 either simple or compound, the simple being a solitary animal, with a 

 single mouth and its visceral cavity ; the compound, a cluster, present- 

 ing as many mouths externally as there are polyps combined, and 

 within, as many visceral cavities. This compound structure proceeds 

 from the capability, above explained, of increasing by buds ; for every 

 coral, however large and numerous the colony, commenced from a 

 single polyp. In some species the bud grows out as a distinct 

 branch from the side of the parent, and branch is thus added to 

 branch by successive buddings from the forming polyps. In other 

 cases, the young continues attached by one side to the parent, instead 

 of forming a prominent shoot, and only their upper extremities appear 

 separate. Large zoophytes are thus formed, consisting of myriads of 

 polyps united to one another by the tissues that surround the visceral 

 cavity of each. 



The several polyps in a compound zoophyte eat and digest sepa- 

 rately, and generally carry on as individuals the processes of repro- 

 duction and aeration ; yet all aid in the growth of the common 

 mass, though each contributes more especially to its own nutriment 

 and the part immediately adjoining. Although their visceral cavi- 

 ties are distinct, there are numerous communications between those 

 of adjoining polyps, and the fluids may pass more or less freely 

 from one to the other. An injury to one part of a zoophyte is felt by 

 the polyps some distance around, but not always through the whole 

 mass. On pressing the tip of a branch of a large Alcyonium, in 

 the Feejees, there was an immediate contraction of every polyp 



