in the Animal Kingdom. 1S3 



the part so called, obviously corresponding to the aorta in other 

 animals ; and, according to the above diagram, having a truly 

 thoracic and abdominal locality.* 



Of the development of molluscous animals, we know very lit- 

 tle : enough, however, to render it quite safe for us to extend to 

 them the laws already laid down ; viz. of the heterogeneous ari- 

 sing only out of the homogeneous, and of identity in the marner 

 of histological and morphological separation (the manner of de- 

 velopment),-f- whatever may be the direction which the latter 

 takes, and however limited its degree. 



Even to Zoophytes, the same laws may be applied. The 

 Germinal Granule of the Polype a homogeneous, shapeless mass 

 separates into a softer portion, on the one hand ; and a more 

 rigid, a horny, or calcareous substance, on the other ; and as- 

 sumes its proper, more or less special, form. Even shoots 

 themselves those, for example, of the Hydra J are at firs 

 simple swellings, then cone-like, afterwards somewhat cylindri- 

 cal, and gradually become funnel-shaped, like the parent : pro- 

 cesses then appearing wart-like, at the circumference of the 

 common cavity, and these by degrees elongating into arms. 



The whole animal kingdom then, (perhaps all organized 

 beings ?), may be considered as directed in development by the 

 above laws ; and all animals present besides, the antithesis of an 



* The Germinal Membrane separates, as well in invertebrated, as in verte- 

 brated animals, primarily into a Serous or Animal, and a Mucous or Vegeta- 

 tive lamina; between which, sooner or later, there is found a third, tjic 

 Vascular lamina (Valentin, 1, c, p. 605). 



The above figure (10.) is not intended to present iheform of any of the 

 Arthrozoa. The form, indeed, of an Osteozoon, has been as far as possible 

 adopted, in order to admit of an easy comparison of corresponding parts; the 

 only purpose here, being to shew the appropriation of the Animal layer of the 

 genninal membrane in the two Classes. We do not at present enter into any 

 comparison in /orro, of parts of the external skeleton of the Arthrozoa, with 

 the osseous system of Vertebrated animals (Osteozoa). 



t See Von Bar's researches on Snails, already mentioned ; also those of 

 Stiebcl and Carus, alluded to by Burdock, Physiologie als Erfahrungswissen- 

 schaft, Band ii. S. 179-180. 



Cartu, plate i. fig. 1. Burdach, 1. c. p. 164-166. 



