in the Animal Kingdom. 131 



be said to differ in different animals ; in manner, it remains the 



same.* 



Secondly ', Of some of the Invertebrata. 

 The following diagrams will illustrate different directions of 

 development, though the manner be the same. 



Ideal Transverse Sections, shewing the Structures formed out of the 



Animal layer, respectively, 



Of the Osteozoa (Vertebrata). Of the Arthrozoa. 



Fig. I). Fig. 10. 



Upper tube 



a, Central portion of the nervous sy- 

 tem ; situated in the upper part of the 

 Animal layer. 



6, Arches of the vertebrae, some of the 

 cranial bones, &c. (part of the inter- 

 nal skeleton.) 



c, Fleshy layer. 



<J, Skin. 



Under tube 



e, Ribs, lower jaw, &c. (part of the in- 

 ternal skeleton) ; the other parts of 

 this tube, as c and d of the upper tube. 



(/, Mucous tube.) 



Upper tube, incomplete, viz. 



o, Situation of what there is, corres- 

 ponding to the central portion of a ner- 

 vous system : situated in the /ouwpart 

 of the Animal layer. 



b, External skeleton, se- 

 creted from the skin, 



forming an 

 Extremity, a 



Mandible, 

 &c. 



c, Fleshy layer, such as 

 it is, 



d, Skin, 



Under tube 



e, External skeleton, secreted from the 

 skin ; the other parts of this tube, as 

 c and d of tbe upper tube. 



(/, Mucous tube.) 



The Vascular tube is not shewn in the above figures. 



pie, as the Cephalopoda of the Class Mollusca, or the Crustacea of the Class 

 Articulata, into Fishes of the Class Vertebrata. As well might it be said, 

 that branches divergent at a tree's root, because they retain some characters 

 in common, can be coincident in their terminal localities. 



There are, however, certain systems of organs more or less common to 

 all beings. Among these are especially the nutritive or appropriative organs; 

 resemblances between which, therefore, in corresponding stages of develop- 

 ment, may be conceived to extend to existences of almost every kind. It has 

 been justly said by Burmeister, that Osteozoa (Vertebrata), uniting in 



I* 



