LECTURES ON EMBRYOLOGY. 



LECTURE VI 



L r/ow proceed to examine the great group of the 

 animal kingdom, which Naturalists have desig- 

 nated under the name cf Articulata, There ani- 

 mat3 are remaikable for one peculiar feamre of 

 their structure ; the body consisting of a series of 

 joints rnoveable upon each other, to which are fre- 

 quently added rnoveable appendages, sometimes 

 subdivided into joints, which are rnoveable also. 

 This is the common character of all Articulata, 

 nnd upon Plates IV, V, VI, VII, IX, X and XI you 

 see various forms of this great type. 



[PLATE TV R.\T-TAILKT> WORMS 1 



VI L'"JSIER ] 



The Articulata have been divided into three 

 classes : Crustacea, as crabs, lobsters and a'll the 

 animals like them; Insects, as butterflies, beetles, 

 flies; and Worms, the worms which live free in 

 the water or in the soil, and also the parasitic and 

 intestinal worms. 



These three classes differ in their structure as 

 well as rs their general form, and they have been 

 placed in our systematic works ia an order which 

 deserves particularly to attract our attention. 



The Crustacea are placed highest in the series of 

 Articulata, and the Worms lowest^ and between 

 them, the Insects, so numerous and so exceeding- 

 ly diversified. In the opinion of Naturalists, this 

 order of succession agrees with the complication 

 in structure of these animals. And they insist 

 upon this order as really indicating the natural 

 gradation among them; the Crustacea being con- 

 ilJered highest, owing to the perfect development 

 of a heart and a regular circulation, and also 

 owing to the concentration of the nervous system 

 and the combination of its elements. The want of 

 a regular circulation in the Insects has been the 

 reason why they have been placed in the second 

 rank. The Worms, from the uniformity and num- 

 ber of their rings, to which are attached feet-like 

 appendages almost as numerous as the rings them- 

 selves, have been considered as the lowest. 



Now in this order of succession-, to which Natu- 

 ralists have specially devoted their attention, 

 which they have investigated with particular refer- 

 ence to a natural classification, I think we have i 



another instance of a mistaken view of the 

 ject, derived from a mistaken estimation of an- 

 atomical characters. I am prepared to show that 

 Crustacea are not the highest-; that Insects should 

 be placed at the head of Articulata; and that they 

 are in every respect the highest. And after the 

 grounds upon which I intend to place them high- 

 est have been illustrated,, I expect it will be found 

 that the anatomical structure agrees here again 

 with the order which the metamorphoses actually 

 indicate; and that it was a mistaken view of the 

 complicated structure of the Crustacea which in- 

 fluenced Anatomists, and induced them to place 

 Crustacea highest. 



Before, however, I can go through this compar- 

 son, I must illustrate in detail the different classes 

 of this great group ; otherwise my comparisons and 

 my grounds would scarcely be intelligible, 



I shall devote this evening to the illustration of 

 that one class which I consider as highest among 



