136 ZOOPHYTES. 



III. All propagate by ova, which are principally liberated by decay 

 of the prolific product. 



IV. The embryo requires a long period for the attainment of maturity. 



V. Maturity is gained by all towards the commencement of the 

 summer season. 



VI. No sensible metamorphosis is undergone by any of the race, 

 farther than evolution of additional hydra? from the sole bearing the first 

 from the ovum of the Cristatella ; and of additional tentacula, with ad- 

 vancing age in all. 



The principal discrepancies consist : — 



I. In the different formation of the three products. 



II. In the Cristatella being endowed with a locomotive faculty. 



III. In the larger size, and different form of its ovum. 



IV. In the diffusion and adhesion of the stratum of the Alcyonella. 



V. In the arborescent form, and tubular structure of the Plumatella. 



VI. In the position of its ova within the cavities of the arborescent 

 parts. 



VII. The ovum of the Cristatella is the largest, that of the Pluma- 

 tella the next, and the ovum of the Alcyonella the smallest. 



Plate XXXI. — Plumatella repens. — Adult specimen affixed to a stone from 



Fenton tower. 

 Plate XXXII. Fig. 1. Plumatella repens, specimen on the leaf of the Water 



Plantain. 



2. The same, shewing the peculiar formation of the skeleton . 



3. Hydra of the same. 



4. Ova of the same. 



5. Plumatella repens, another specimen. 



G. The same, shewing the tubular receptacles of the hydrre. 



7. Hydra of the same. 



8. Plumatella repens on a leaf of the yellow Iris. 



9. Hydra of the same. 



10. Ramifications of the lower portion of the same, contain- 

 ing ova, as on October 17. 



