1871.] 403 [Wilder. 



If we could confine ourselves to the adult Mammalia, the answer to 

 this would be easy, for no member of this class is known to possess 

 more than two pair of organs which answer to the common idea of 

 "limbs"; the same is true with the reptiles, the birds, and the 

 amphibia, but if we include the fishes, there is room for difference of 

 opinion. 



Huxley (251, 61,) and Eolleston, (284, xxxn), state that there 

 are only two pair of " articulated limbs ;" and this is the opinion of 

 nearly all anatomists ; but Parker, (292, 3), seems to include the 

 ordinary membra in the same category with the median fins ; Hum- 

 phrey, (248, 65,) is more explicit and holds that '* each limb of the 

 higher animals corresponds with a lateral factor or factors of the 

 mesial fin of the fish and would, if development had proceeded in a 

 similar manner, have united with its fellow into a mesial organ." Cle- 

 land (65), advances the view that " the suspensorium and lower jaw 

 form an arch corresponding with the limb arches, and the opercular 

 apparatus of fishes consists of appendages attached to it ;" while 

 Owen (20, 333 and 63, 1, 102), not only includes under the general 

 title of " diverging appendages," the pectoral and ventral fins (or 

 "limbs"), the " branchiostegals," the " operculars" and the "ptery- 

 goids," but also (20, 269; 63, 1, 30, and 63, 2, 18) enumerates there- 

 with the slender or flat processes projecting backward from the ribs in 

 some fishes, crocodiles and birds; and further adds that "the true 

 insight into the general homology of limbs leads us to recognize 

 many potential pairs in the typical endo-skeleton," (20, 270). 



Now it must be admitted that the facts of development as at present 

 understood, are not wholly opposed to the above views of the "general 

 homology of limbs"; and Wyman, after a most admirable exposition 

 of the case (55, 264) says " we believe there is ground for the hypo- 

 thesis that limbs belong to the category of tegumentary organs." 1 

 But it ought also to be considered that this conclusion is based chiefly 

 upon the apparent identity of the membral buds with the ridges which 

 afterward give rise to the median fins; and this involves the great ques- 

 tion of the relative value of development and of position for the deter- 

 mination of homologies ; in the present case, if we allow that the hom- 

 ology between the median and the lateral appendages of fishes is as 

 complete as that between the two pairs of lateral appendages them- 

 selves, upon the ground of primitive identity of structure, then must 



1 Oken, (285, Par. 3337), called them " tegumentary members." 



