l894-] NEW-YORK MICROSCOPICAL SOCIETY. 45 



III. The Classes of Vertebrata. 



A. Fishes. 



In certain members of this class we find conditions which have 

 undoubtedly been inherited from invertebrate ancestors. Thus 

 in the outer epidermic layer of many Fishes {Aiiiphioxi/s, e.g.) we 

 find a striated border, which can be imagined to consist of 

 coalesced cilia, and in the larval condition we find the free-mov- 

 ing cilia themselves on the outer surface of the epidermis (Fig. 

 I, S C). Here, as in many other instances, we can see gradual 

 transitions from lower to higher forms. 



Glands, such as we find in higher vertebrates, are usually not 

 present in Fishes. The skin secretions which we do find come 

 from single cells or canals (Fig. r. A). The fluids which they 

 contain probably protect the skin from the action of the water or 

 ward off the attacks of fungoid growth ; and it has lately been 

 determined that certain of them function also as sense organs. 

 Other secreting cells are also present, the so-called '"'' goblet cells'' 

 (Fig. I, K), whose function has not been definitely determined. 



The most marked characteristic of the integument of Fishes is 

 in the scales. These lie in connective-tissue pouches of the derma, 

 and are formed as ossifications of the latter. In the higher types 

 of Fishes they are covered by the epidermis throughout life, 

 but in Ganoids (Gar-pikes, etc.) and Elasinobranchs (Sharks and 

 Rays) this is only the case in the larva. In the adult they are 

 free and projecting. The primitive form of the common fish 

 scale, as we see it in the Perch, for example, was probably an 

 ossification in the derma, which we call the basal plate with 

 projecting processes, the derm denticles. The transitions which 

 these have undergone from one form to another constitute a very 

 interesting series. In many Fishes, especially fossil, they form 

 a complete protective armor by their fusion, as in the well-known 

 armored South American catfishes. 



The next factor to consider is pigment. This always originates 

 in the derma, and to it is due coloration. In endeavoring to ac- 

 count for its presence in the epidermis it has been asserted and 

 observed that white blood corpuscles carry pigment granules to 

 the outer layer, where they take on amoeboid movements, and 

 then break up into many small pigment-containing particles, 



