94 SPECIAL CONVERGENCE 



Herpestes, the Indian mungoose, has a well- 

 defined, horizontal pupil in the daytime, becoming 

 round at night (Fig. 7, Frontispiece). The allied 

 genus Suricata, the South African meerkat, has 

 a similarly shaped pupil, shown very clearly in 

 the specimens at the London Zoological Gardens. 



Hubrecht {I.e., 1908) has given reasons for 

 believing that the cartilaginous fishes occupy a 

 side branch of the vertebrate stem, and he 

 goes so far as to suggest a radical change in 

 the classification of vertebrates, dividing them 

 into four super-classes : Cephalochordata {Ampki- 

 oxus), Cyclostomata (lampreys, etc.), Chondrophora 

 (sharks, etc.), and Osteophora (bony fishes and 

 higher vertebrates). In view of this weighty 

 opinion, the a priori probability that the nicti- 

 tating membrane of some sharks (Carchariidae), 

 which is an accessory protection for the eye, 

 sweeping over the surface of the eyeball, has 

 no genetic connection with the functionally 

 equivalent membrane of many of the higher 

 vertebrates, is greatly strengthened. 



Bony fishes have no movable eyelids, but 

 transparent adipose eyelids are sometimes present, 

 composed of an anterior and posterior membrane 

 or of a continuous circular membrane perforated 

 at or about the centre. Both the Grey Mullet 

 family (Mugilidse) and the Herring family 

 (Clupeidse) are respectively differentiated into 

 groups by the presence or absence of adipose 



