364 PROCEEDINGS OF THE ACADEMY OF ' [1887. 



The degenerative processes made manifest in ontogeny, often undo 

 the synthetic or constructive morphological work, which has been 

 accomplished during phylogeny. This seems to be the ease in these 

 extremely modified forms of Gold-fishes, in which, indeed, there is 

 palpable evidence of great cranial modification, similar to that seen 

 in domesticated races of Pigs and in the Japanese Lap-Dogs {Dyso- 

 d'us, Cope), in all of which, as in these fishes, the anterior cranial 

 and facial bones have been greatly modified. 



The preceding explanation seemed necessary in order to empha- 

 size the doctrine that paired fins might be evolved from the sides of 

 the tail as supposed by Dohrn and Mayer, by the median fusion of 

 the ventral fin-folds, which, according to their views, were primor- 

 dially double and lateral. It follows from this doctrine, that the nerves 

 passing to the musculature of the anal and caudal pairs of fins, must 

 be considered as forming two additional plexuses, neither of which 

 can by any mode of torturing the facts, be rendered homologous 

 with those Avhich supply the pectoral or ventral pairs. 

 III. Consequences of the preceding data. 



The facts presented above seem to me to lead to the conclusion 

 that the ichthyopterygium in Fishes is very far from representing 

 the same or homologous structure ; a view which the ontogeny of 

 the higher vertebrates fully confirms. While the first point has 

 been admitted by INIivart, Huxley and others, the second has not 

 received the attention which its importance demands. The fact that 

 the rudiments of the paired limbs do not normally arise in a homo- 

 nymous position or at the same points along the a?;is in Mammals, 

 Birds, Reptiles, Amphibia, etc., and without any manifest action of 

 translocation during development, seems to the writer to preclude 

 the possibility of our assuming that there has existed a common and 

 exactly homologous, ancestral chiropterygium, from which the limbs 

 of vertebrates, from Amphibians ujjward, have been evolved. There 

 are many difiiculties in the way of an answer to this question. 

 First of all, the universally admitted fact that similar structures may 

 be developed under similar conditions in widely dissimilar types. 

 Secondly, the utter want of exact homology when the pro- meso- and 

 mctapterygium are compared. Thirdly, the few unassailable facts 

 which we possess in regard to undoubted instances of the transloca- 

 tion of limb rudiments. Fourthly, the origin, by coalescence, of an 

 indefinite number of radii to form the pro- meso- and mctapterygium. 

 Fifthly, the variations to which this coalescence is subject ; that is, 



