46 JOURNAL OF THE [April, 



which are taken up by the epithelial 'cells. The distribution of 

 pigment over the body varies with the species and individual. It 

 is also subject to changes in environment, and is under direct 

 control of the nervous system. That it changes in order that 

 the animal may adapt itself to its surroundings, has lately been 

 demonstrated in the case of the common English Sole. As is well 

 known, the color of its upper side approximates very closely the 

 tint of the muddy bottom upon which it lives. However, when 

 placed under conditions which permit the access of light to the 

 lower as well as the upper side of its body, pigment will also be 

 developed on that side which formerly showed no trace of it. 



We now take up a very important derivation of the integument 

 — sense ori^afis. Their main function is probably the perception 

 of mechanical irritations of the surrounding water, but they may 

 also have to do with the perception of sound. As elements we 

 have two kinds of cells : rod-shaped sensory cells, connected by 

 nerve fibres with the central nervous system, and the supporting 

 cells, which lie between the others and serve as connecting and 

 isolating material. The surrounding medium is always kept moist 

 by various secreting cells In those animals which give up an 

 aquatic life in the course of their development and come to live 

 on land, the end organs of the nerves pass further inward, the 

 rod-shaped cells disappear, and we have two kinds of nerve end- 

 ings in the skin : terminal ganglion cells and free nerve endings. 

 With Fishes we must include Amphibia in the consideration of 

 these sense organs, as the two types are very closely related. 

 " They consist of a central mass of cells, arranged in the form 

 of a rounded and depressed pyramid, and of a peripheral mass 

 grouped around the former. The central cells are in connection 

 with nerve fibres, and each bears on its free end a stiff, cuticular 

 hair ; these are to be looked on as the proper sensory cells, and 

 the others merely as a supporting medium." Where these hairs 

 project freely from the epidermis they are surrounded by a deli- 

 cate, protective, hyaline tube, which opens into the surrounding 

 water, and into one end the sensory hairs project. These organs 

 are at times distributed over the whole body, but as a rule only 

 in certain well-defined tracts ; those along the sides from the 

 head to the tail form the so-called organs of the lateral line. 

 Others are found in depressions or canals formed by scales, and 



