vm ORIGIN OF LIMBS 113 



Ungulata than the Carnivora, and that there is some truth in the 

 old expression — sea-hog or sea-pig, Meerschwein, Marsouin — 

 applied to the porpoise itself, I believe derived from Porc-poisson. 



Their origin is, however, at present a complete mystery, and 

 palaeontology throws very little light upon it. The earliest known 

 Cetaceans, the Gengloda of the late Eocene, are still imperfectly 

 known, although certainly in some points about the dentition and 

 cranium more generalised mammals than any existing forms ; of 

 their limbs we know next to nothing. The Sirenia (Dugongs and 

 Manatees) form a totally distinct type, with nothing to do with 

 either Cetacea or seals, except in adaptations to similar conditions 

 of life — the mere resemblance of a bat to a bird. Their pelvis 

 is also very rudimentary, and no existing species has any trace of 

 hind limb ; the extinct Holitherum, however, had a little pelvis and 

 small styliform femur. I cannot form the slightest guess at 

 present as to what other mammals they are related to. Palaeon- 

 tology does not help us here either ; but when we consider the 

 enormous advances that have been made in this branch of the 

 subject as regards certain groups — the Ungulata of North America, 

 for instance — within so few years, we can hardly say what may 

 not be still to be discovered. 



I think that I have answered all your questions as fully as I 

 am able. 



Professor Flower to the Duke of Argyll 



June 8, 1883. 



I think that I was able to answer satisfactorily the question 

 you once asked me, as to whether the rudimentary hind limbs 

 were disappearing or incipient structures ; they must certainly 

 be the former. Limbs always commence by their most distant 

 or superficial parts appearing just as folds or outgrowths of skin 

 — this is the only form in which they could be of any use to the 

 animal — afterwards they get strengthened by the internal struc- 

 tures and connected with the skeleton. In all the higher verte- 

 brates they are developed in this way. 



In disappearing the process would naturally be the reverse. 

 The outer part would go first, or when once so shrunken as to 



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