150 ZOOPHYTES. 



Plate XXII. Fig. 7. Prolific vesicle, having discharged its contents in a mass, 

 proving abortive. 



8. Another. 



9. Planulse from the vesicles. 



10. Nascent Sertularia originating as a spine from a planula. 



11. The same, farther advanced, with the hydra budding in 



its cell. 



12. The same ; the hydra now mature, displayed from its cell. 



13. Specimen illustrating the regeneration of hydrse. 



All the figures of this Plate, except the first, enlarged. 



§ 2. Sertularia Abietina — The Fir Sertularia. — Plates XXIII. 

 XXIV. XXV. — Perhaps no animal product is exempt from individual 

 distinctions, if those which are inscribed as the nearest kindred exhibit 

 peculiarities. When such peculiarities are decisive in several, they con- 

 stitute a species; and where some common features apply to several 

 species, they are united as a genus. It is only by examining a number of 

 specimens that the facts are discovered ; but much difference of opinion 

 must ever subsist as to what distinctions are sufficient to establish either 

 genus or species ; and it is not to be denied that superficial views have 

 misled many naturalists. The presence or absence of an organ, the posi- 

 tion and number of the various parts, their supposed use, their transience 

 or permanence, have been all leading guides. Varieties are determined 

 from the fainter differences. 



The Sertularia abietina is thus named from its resemblance to some 

 kind of fir, in conformity with the practice of comparing objects less 

 known to those more familiar. 



It rises nine or ten inches high, by a slightly waving stem, with 

 branches diverging from each side in alternate arrangement, so that the 

 extreme expansion of the product is about three inches, somewhat above the 

 root. The branches shorten upwards, in proportion to their height on the 

 stem, until only a single alternate cell borders the highest. The sides of the 

 whole stem from the root to the summit, and of all the branches from the 

 origin to their extremity, are clothed with a row of cells, also in alternate 



