104 ON THE MORPHOLOGICAL CONSTITUTION OF 



The bony rays developed in the metamyotomic laminte of 

 fishes exhibit the most elementary forms of actinapophyses. 

 Here again I must differ from Professor Owen, who limits 

 the number of these "diverging appendages" to one — gene- 

 rally attached to the plem-apophysis — on each side of the 

 vertebra. This " epipleural element" he considers to be a part 

 of the endo-skeleton, while the additional radiating bony fila- 

 ments he refers to the exo-skeleton, and recognises in them a 

 manifestation of the principle of "vegetative repetition." 

 AVhile I admit that the so-called "epipleural spines" are the 

 most constant of these bones, yet, as the others are developed 

 in the same fibrous membrane, which has, moreover, no primary 

 relation to the dermal system, I cannot see on what grounds 

 they can be excluded from the endo-skeleton. As, again, I 

 cannot avail myself of the principle of " vegetative repetition" 

 in a morphological inquiry, and as I find all of these " addi- 

 tional ribs" connected with important modifications of the 

 myome, I account for their presence teleologically, and hold, 

 therefore, that they must also be explicable morphologically. 



The question as to the typical number of actinapophyses 

 in a sclerotome cannot, it appears to me, be determined in the 

 present state of the science. Their existence and general 

 morphological relations having been ascertained, the conditions 

 which determine their position and number must remain for 

 future inquiry. 



On these grounds I cannot, with Professor Owen, regard 

 the branchiostegal rays on each side collectively as a single 

 " diverging appendage." I not only recognise on each side of 

 the hyoidean arch of the osseous fish one series, but a double 

 series of actinapophyses. This double arrangement of the 

 brancliiostegal rays has not, so far as I know, been recorded. 

 One series of these rays is attached along the outer, and 

 therefore morphologically anterior surface, and the other along 

 the inner, and therefore posterior surface of the cerato-hyal ; 



