118 On the Microscopical Siliceous Polycystina of Barbados, 



distinctly as we reject such a supposition in fossil shells and in fossil 

 bones of mammalia ; though their cruciform structure (Kreuzformeri) 

 might primd facie afford some shadow of ground for such a suppo- 

 sition. With regard to the possibility of their being of a vegetable 

 nature, although Phytolitharia, chiefly Spongia and Tethya, might 

 afford some analogical points of comparison, the author (Prof. Ehren- 

 berg) rejected such a conjecture as early as the year 1838, since 

 his numerous examinations of sponges from all seas and all geolo- 

 gical formations where they had hitherto occurred, made him ac- 

 quainted with hundreds of forms doubtless of a regular structure and 

 easy of recognition, but never with such forms as indicated develop- 

 ment of organization. The great number of Polycystina also fur- 

 nishes arguments opposed to such a supposition in the structure of 

 their shields or shells ; and as there are recent specimens existing in 

 the mud at the bottom of the sea, and which possess distinct parts 

 of organization, we are authorized at coming to a similar conclusion 

 with regard to the origin of those in a fossil state. The regular 

 apertures and articulation of the minute shells distinctly bespeak an 

 independent animal structure and development. The large aper- 

 tures at the extremity of the body possess no analogy among plants, 

 but occur very commonly among animals." 



With respect to the affinities which these minute forms of ani- 

 mals bear to the known classes of animal life, Professor Ehrenberg 

 has again assumed that fundamental principle which he adopted 

 in 1835, when he brought before the Royal Academy his clas- 

 sification of the animal kingdom*, namely "a development every- 

 where equally perfect f." Several circumstances at that time 

 alluded to have since been determined more in detail, but the 

 principal groups and characteristic features have remained un- 

 changed. Accordingly the siliceous-loricated organic forms from 

 the rocks in Barbados differ alike from Polygastrica and Poly- 

 thalamia, but develope an important relation to these two groups, 

 which Professor Ehrenberg considers, not upon conjecture, but 

 from actual investigation, to form two separate types of forma- 

 tion. The siliceous shell connects them with the Polygastrica, 

 the intestinal structure of which has a radiated form ; but the 

 transverse articulation, and the cellular arrangement of their 

 structure, point to a connexion with those which have not a 

 radiated but a tubular formation of the intestinal canal, and 

 the shields of which are always calcareous, and not siliceous. As 

 the intestinal structure of a living form of Polycystina has not 

 as yet been examined, Professor Ehrenberg infers, from the 

 physiological formation alone of the whole numerous group, a 

 close analogy to the Moss-animalcules (Bryozoa) and chiefly to 



* Die Akalephen des rothen Meeres und der Organismus der Medusen 

 der Ostsee. (The Acalephce of the Red Sea, and the Medusa of the 

 Baltic.) 



f Das Princip einer "uberall gleich vollendeter Entwicklung." 



