INTRODUCTION. Ixi 



tail in the history of the discovery, in order to do 

 justice to those whose original and independent observa- 

 tions led them to break through the trammels of precon- 

 ceived notions, and, notwithstanding much opposition 

 and some misrepresentation, persevered in prosecuting 

 the investigation until the truth of the doctrine has been 

 universally received.* 



It has not been my object, in the present Introduction, 

 to enter into the details of the anatomy and physiology of 

 the class of animals of which it treats. It has been con- 

 sidered sufficient for my present purpose to offer a very 

 slight sketch of the principal organs and their functions, 



* During the passage of part of this introduction through the press, I received 

 a communication from my friend Mr. Couch, containing some new observations 

 on the development of the lobster. From these observations, and others made 

 on Caprella and other forms, Mr. Couch comes to the following conclusions, 

 which are strongly confirmatory of the doctrine of arrested development, and 

 are, in that point of view, very interesting. The original paper was read at 

 the Royal Cornwall Polytechnic Society. 



" So far as my observation has extended, it appears probable that the meta- 

 morphosis of the young in their progress to adult growth is not universal in all 

 Crustaceans ; but, on the contrary, that the families in which the eyes are always 

 sessile in their adult growth, and which do not exuviate or voluntarily throw off 

 their limbs, are in the habit of producing their young perfectly formed ; and an 

 opportunity that has occurred to me of observing the process of early develop- 

 ment in the common lobster will tend to establish the existence of a law of 

 Nature as applicable not only to it, but probably also to all the genera of this 

 extensive family or class that is, the long-tailed Crustacea which law is, that 

 the greatest extent of metamorphosis is in those genera which are of the highest 

 rank in the series that is, the short-tailed, or crabs that, even at their birth, 

 the long-tailed genera as the lobster approach more closely to the ultimate 

 form of the parent ; and what is still more extraordinary than all beside that 

 so long as the lobster in particular, retains the eyes sessile, the progress of develop- 

 ment and growth is conformed to what is the perpetual mode of growth of the 

 permanently sessile-eyed races; and it is only when the crust has become fully 

 extended and hardened, and thus the exuviation is rendered necessary, that the 

 eyes become elevated on footstalks, and the adult form and habit are completely 

 established." 



