XXXIV 



Or, is the question rendered any more easy by first assuming that the Elas- 

 mobranchiates are "highest" and therefore (but why ?) next to the Batra- 

 chians, and then successively arranging the Ganoids, and the Teleosts, still 

 retaining the last nearest to the Marsipobranchiates 1 ? Admitting that the 

 Dipnoans and (causa argumenti) the Elasmobranchiates are the nearest 

 allies of the Batrachians, are the Teleosts the nearest allies of the Marsi- 

 pobranchiates ? Are they in any essential respect more like them than are 

 the others ? Does the study of their homologies receive any light from 

 the juxtaposition ? Is any advantage gained ? On the contrary, are not 

 the questions remaining still more involved by reason of such sequence ? 

 Is not the natural sequence from the generalized to the specialized unna- 

 turally interrupted and reversed ? The answers are not dubious. 



Again recalling the universal admission of the " low" or, rather, genera- 

 lized attributes of the Leptocardians, we have in the ciliated clefts of their 

 pharyngeal sack the first (known) rudiments of a specialized branchial 

 apparatus; an enormous advance is exemplified in the branchial apparatus 

 of the Marsipobranchiates (1. Hyperotreti, 2. Hyperoartii) which never- 

 theless is (it may be safely said) obviously homologous — i. e. homogenetic — 

 with that of the Leptocardians ; another advance, less but still very de- 

 cided, is exhibited in the branchial apparatus of the Elasmobranchiates, 

 while in the Chondrostean and other Ganoids successively, more specialized 

 phases are developed, and all in the direction of the Teleosts. We have, 

 in these phases, an apt exemplification of the same concentration towards 

 and in the head as is exhibited by the Tetradecapod and Decapod Crusta- 

 ceans in their segments and appendages, and which have furnished to the 

 learned Dana the first foundations for his hypothesis of cephalization. 

 And from whatever standpoint we view the series of fishes, the facts of 

 structure, of homologies, and of affinities receive the most light by their 

 exhibition in the sequence advocated, i. e., Leptocardia, Marsipobranchia, 

 Pisces elasmobranchii, Pisces ganoidei, and Pisces teleostei. 



And while most naturalists would probably not be indisposed to admit 

 the natural character of the sequence up to the Dipnoans, the desire to 

 have those forms in juxtaposition to the Batrachians and an exclusiveness 

 of attention to that question might result in cutting the gordian knot by 

 effecting that juxtaposition and practically ignoring the other difficulties. 1 



Two questions are principally involved in this consideration. 



First. What is the fish most nearly to the Batrachians, and consequently 

 to the quadruped vertebrates generally ? 



1 Probably some of tbe results in systematic zoology are attained by (1) commencing 

 with Man as the highest, and then (2) approximating successively certain forms, on 

 accouut of real or supposed affinities, and with little care as to where other forma, 

 whose affinities are less obvious, may lead. 



