iS6 STUDIES IN THE EVOLUTION OF ANIMALS 



Trygon brevicaudata, there are two specimens, id) with a smooth 

 skin, seven plates on dorsum of tail, and minute scattered plates 

 on other parts of the tail ; [b) also with a smooth skin, but with 

 several spots on both sides, and only eleven plates on dorsum 

 of tail besides other minute tail-plates. 



This series of fishes is very instructive, and there is no good 

 reason to doubt that in the latter the spots are partial vestiges of 

 the more complete armour of Urogymnus asperrhnus. The back- 

 armour and tail-armour of the latter would lead us on, in the course 

 of ages, to the huge carapace and curious tail-armour of the 

 Glyptodonts. 



There are many spotted Sharks, and the spinous Shark {Echin- 

 orhinus spinosus Gmelin)'^ is dotted with spinous plates, some 

 isolated, others confluent in groups. It seems probable that these 

 are only vestiges of an ancestral and more complete carapace. 



Then there is another fish in the Natural History Museum which, 

 in this connection, is very instructive. It is the Serfanus gigas of 

 Muscat. It is a large scaly fish in one of the middle cases. The 

 horny scales of fishes can only be considered as a modification of the 

 bony armour-plates, like those of the bony Pike and extinct Ganoids. 

 Well, the large body scales of this Serranus have each a black dab. 

 On the cheeks of the fish ^ the scales become thinner and thinner, 

 and almost amalgamated with the skin, each scale still retaining 

 the black dab. Then on the lips of the fish the scales disappear, 

 but the black dabs or spots remain. 



Of course the spots in this case are not exactly identical in 

 genesis with those of the Jaguar skin, unless we suppose that the 

 Glyptodontoid ancestors of the latter, besides their bony plates, 

 had also a corresponding set of horny plates, like those of Arma- 

 dillos, and spotted analogously to the spotting and marking of the 



^ Science and Ait Museum, Edinburgh. - Technical terms are here unimportant. 



