1910.] CAUDAL FIN OF THE TELEOSTOMI. 501 



at the Naples Zoological Station. The many frienrls who have 

 ,sup2)lie(l me with matei'ial and sugge.stions also luive my best 

 thanks. ¥ov the identification of most of the specietj 1 am greatly 

 indebted to Dr. Lo Jiianco of the Naples Zoological Station. 

 Lastly, I am deeply grateful to the. Birmingham Natural History 

 and Philosophical Society and others, for grants without whicii 

 the work could scarcely have been done. 



The dissections have been carried out as carefully as possil)le 

 under the microscope, and it was found necessary in most cases 

 to render the specimen transparent by some clearing agent such 

 as turpentine or xylol, in order to see exactly how the vertebral 

 column ended, and to clear up any other doubtful points. 



In reviewing the literature on the subject of caiidal fins, the 

 very numerous casual references must be omitted for the present. 

 Perhaps the earliest definite work relating to fishes' tails is that 

 of Agassiz in 1833, in which the author recognized two types of 

 caudal fin, the heterocercal and homocercal ; the former term still 

 retains its original meaning, but the latter was only used to 

 indicate an externally symmetrical fin as distinguished from the 

 asymmetrical heterocercal form. In a geological contribution by 

 McCoy in 1848, the term " diphy cereal " first appeared to desig- 

 nate the truly symmetrical caudal fin ; it is interesting to note 

 that Cope in 1871 coined the term "isocercal" to mean the same 

 thing, in ignorance, as that author states, of McCoy's paper. 

 Stannius, in a text-book on the Vertebrata, published in 1854, 

 gives considerable attention to the tail-fin ; he refers to a very 

 lai'ge number of Teleosts, but with questionable accuracy. The 

 most interesting feature of his remarks concerns his belief, which 

 seems to be true, that the supports of the fin-rays ai'e formed of 

 arches and radials fused ; Belone is cpioted in sujiport of this 

 view. 



But it was in 1859 that Huxley first gave a correct description 

 and interpretation of the homocercal tail ; he exposed the f.ilse 

 symmetry of form in Gasterosteus, and traced its development. 

 It is unfortunate that the promised account of the development of 

 the eel's tail never appeared, for the slight i-eference made to this 

 form is of doubtful accuracy, due, no doubt, to only a superficial 

 examination. Yery soon followed (in 1860) an excellent essay 

 on caudal fins among Ganoids and some Teleosts by Ivolliker, 

 accompanied by valuable figui'es which have been i-eproduced 

 almost universally since. Lotz followed in 1864 with a paper 

 containing little new work. 



A revival was given to the subject in 1878 by Alex. Agassiz in 

 a short paper on the development of the tail of the flounder ; his 

 remarks had the effect of raising the important (juestion df the 

 true morphology of the homocercal caudal fin. In 1882, 

 E. T. Newton read a paper on " Fishes' Tails " before the Quekett 

 Microscopical Club ; this consisted of a general I'eview of past 

 work, together with a desci-iption of the tail of the sprat ; the 

 paper included an incori-ect figure of the caudal fin of the cod. 



39* 



