GENERAL STRUCTURE OF ZOOPHYTES. 13 



7. Reproduction takes place both by means of ovules and buds. 



The ovules form as above stated, and either pullulate from the sides 

 of the animal, or find exit through the mouth. Soon after ejection 

 (and sometimes before), each ovule produces a young polyp, which 

 swims free for a while, and then, with few exceptions, attaches itself 

 to some support, where, in very many species, it passes the rest of its 

 existence. 



The mode of budding, bears some analogy with the budding of 

 leaves or flowers from a plant. In many instances, the bud first 

 appears as a slight swelling on the side of a polyp ; after enlarging 

 for awhile, a new polyp is finally developed, with tentacles and visce- 

 ral cavity complete ; this cavity is sometimes continuous with that 

 of the parent ; at others, it becomes separated at base, and, at others, 

 still, the whole young polyp becomes entirely detached from the 

 parent. There is some variety in this mode of reproduction which 

 will be noticed when treating separately of the different orders of 

 zoophytes. 



Buds open from different parts of polyps, either laterally from the 

 base, the sides above, just exterior to the tentacles, or from the disk. 

 Disk-buds, though similar to the others, in principle, are peculiar in the 

 changes they produce and the appearances presented. For since the 

 disk covers the top of the visceral cavity, the new bud which opens, 

 shares in this cavity with the parent, and the two become separate 

 only by gradual growth upward. It appears like a spontaneous sub- 

 division of a polyp, arid is so in the result, though quite different from 

 the spontaneous fission of a monad (^ 7779). 



Besides these modes of increase, polyps may be multiplied from 

 sections artificially made. Some species may be cut into a dozen or 

 more parts, and will make as many perfect polyps, each part possess- 

 ing within itself the power of reconstructing a complete animal. A 

 wound on the side of some budding species (Hydras), instead of being 

 an injury, only opens the way for a cluster of new polyps which soon 

 after sprout from the spot. 



There are thus the following different modes of reproduction : 



1. OVIPAROUS. 1. By ovules proceeding outward from the side of 

 the polyps, singly or in clusters. 



2. By ovules formed from vertical lamellae in the visceral cavity, 

 and ejected through the mouth. The viviparous is but an accident 

 in the oviparous mode ; the eggs within develope in the same 



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