TUNIC AT A. 469 



tria, Uptiotes, Dysdera, Sphodros, Filistata, 

 Oletera, Mygale. 



Order Pulmonaria. 



Respiratory organs consisting only of pulmonary lamelligerous sacs. 

 Cephalothorax unarticulated ; abdomen articulated. 



Phrynid^. Abdomen distinct from cephalothorax. Chelicers 



unguiculate 

 Genera Phrynus, Theliphonus. 

 ScoRPiONiDM. Abdomen indistinctly separated from the cepha- 

 lothorax. Chelicers forficulate. 

 Genera Scorpio, Buthus, Androctonus. 



LECTURE XX. 



TUNICATA, BRACHIOPODA. 



The Articulate series of animals leads the investigator of the ascend- 

 ing course of organic development from the Entozoa to the higher 

 organised worms which circulate red blood, and through the strange 

 and changeable forms of Epizoa and Cirripedia to the Crustacea, the 

 Insecta, and the Arachnida, in which three highest classes of articu- 

 lated animals with jointed limbs, as many diverging branches from 

 the common vermiform root seem respectively to terminate. 



Yet having attained these several summits of the articulate branch 

 of organisation, the inquirer still finds himself at a great distance 

 from any of the Vertebrate forms of animal life. How vast the 

 hiatus which separates the worm from the lamprey, the crab from the 

 tortoise, and the beetle from the bird or bat ! He soon attains the 

 conviction that there is no regular and uninterrupted ascent in the 

 scale of organisation, as Bonnet fancied ; no single progressive series 

 of beings ; no necessitated connection of such, as the Poet believed, 

 who sang, — 



" From Nature's chain whatever link we strike, 

 Tenth or ten thousandth breaks the chain alike."— Pope. 



How strikingly illustrative of the subsequent progress of the 

 science of animal life is this evidence of the creed of the bard of 

 Twickenham, in which he has recorded in imperishable verse the 

 convictions of the most cultivated minds of his day ! 



Not even the insight which we now command into the living forms 



H H 3 



