NOMENCLATURE OF ORGANS. 83 



species of the shark parasites (Pandarus alatus}, he says : 

 " The student who is anxious to see how ingeniously the few 

 and simple organs of this creature can be analysed and re- 

 solved into parts corresponding with the complex organs of 

 the crab and lobster, must consult the interesting memoir of 

 Milne Edwards (in the Annales des Sciences Naturelles, 

 torn, xxviii.) I must acknowledge that the analogies seem 

 not a little imaginary, and the nomenclature derived from 

 them is at least faulty, in so far that it gives, or is apt to 

 give, erroneous ideas relative to function. The feet-jaws are 

 not subservient to manducation in any way ; the animal is 

 suctorial, and requires no jaws, and these organs are used 

 solely to obtain fixedness of place ; while the thoracic feet 

 again are not organs to walk or creep on, but are only calcu- 

 lated for swimming, which, we can conceive, it may often 

 have occasion to do." Although we may admit to its full 

 extent the soundness of Dr. Johnston's remarks in examining 

 an animal per se, we certainly do feel, when investigating the 

 same animal with reference to the structure of the remainder 

 of its class, that the great difficulty with which the>subjectis 

 surrounded ought to make us hesitate before we condemn a 

 series of names which the strictest analogy has proved to be 

 correct. Let us, however, look at the matter with reference to 

 some of the better known examples of the class. Examine 

 a lobster and a crab, and the mouth is found to be exter- 

 nally composed of several pairs of flattened organs, having a 

 transverse motion, and evidently acting as jaws, whilst the 

 large pair of fore legs is terminated by great and powerful 

 claws. Now, examine the spiny lobster, and the claws are 

 no longer to be seen; in their stead a pair of limbs are 

 found, having indeed the same number of joints as claw-legs, 

 but formed like the following legs, and evidently being em- 

 ployed in loc omotion. But will it be said that the least stretch 

 is given to our fancy when we assert that the foreleg of 



