[55] THE EVOLUTION OF THE FINS OF FISHES. 1035 



Dr. Gill seems to lay especial stress upon the statement made by 

 Putnam that there is no caudal chain of interspinous bones developed 

 in Molacanthus, and that their absence justifies him in recognizing the 

 form as distinct from Mola. Unfortunately this character becomes as 

 completely valueless in the light of embryology as all the rest which have 

 been used to define Molacanthus as a form worthy of family rank. As 

 we have already shown, Ostracion hoops has no developed caudal, while 

 Molacanthus has only traces of it as very short and feebly developed 

 rays ; and inasmuch as interspinous bones are always developed upon 

 cartilaginous bases in the form of bars, and since fin-rays may be 

 developed while the interspinous cartilages are still very imperfectly 

 formed, there remains no shadow of doubt in the mind of the writer 

 that the interspinous bones or their cartilaginous matrices were still 

 undeveloped in Molacanthus, or at least so imi)erfectly developed in 

 Mr. Putnam's specimen as to be undiscoverable or very readily over- 

 looked. It thus becomes very easy to regard Molacanthus as merely a 

 stage of the growth of Mola, in which the development of the tail bas 

 been retarded owing to the extraordinary and unique modifications 

 which the type form has undergone. I am, therefore, fully convinced 

 that the absence of developed caudal interspinous bones in Molacanthus 

 is merely a transient embryological character and absolutely worthless 

 in taxonomy. Of this I am so certain, that I will venture to predict 

 that when an examination is made by a competent anatomist, a condi- 

 tion of things approximately like that which I have described will be 

 found to exist. 



Fortunately, I have been able to verify the foregoing prediction, which 

 was written as it now stands a week since. Upon cutting open the skin 

 at the edge of the tail of a specimen of Molacanthus with extreme care, 

 so as not to otherwise injure the specimen, I found the axial skeleton 

 in place, and carefully exposed its parts. I found, as stated by Putnam, 

 the interspinous bones, which support the caudal fin, very feebly devel- 

 oped, if not absent. The spines of the seven caudal vertebrae were 

 developed, but the vertebrae themselves, as well as the spines, were 

 feebly ossified, their bony matter being developed, as usual in young 

 fishes, in a perichondrial and perichordal position, wholly dissimilar from 

 the adult condition. The terminal or floating vertebral centrum is de- 

 veloped, and is very short and bluntly pointed, ending just within the 

 margin of the fleshy part of the caudal fin, and so very near the base of 

 its ray-bearing marginal fold that it is difficult to see how there would 

 be room for caudal interspinous pieces. Yet from my examination I 

 am not certain that when a specimen is examined with the more accu- 

 rate and thorough inethod of microtomy, they may be found as minute 

 cartilaginous elements. They must necessarily be minute, for the nar- 

 row triangular area occupied by them in Molacanthus is not quite a mil- 

 limeter wide and five millimeters long. To judge from the very rudi- 

 mentary condition of the caudal fin in the Molacanthus stage, we should 



