488 ELEMENTARY ANATOMY. [LESS. 



skin placed one on each side between the eye and the nose, 

 as in Cro talus. 



There may be a series of glands in each thigh, with a 

 row of conspicuous openings, called femoral pores, on its 

 inner surface, as in very many Lizards (Lacerta, Monitor, 

 &c.), or in the armpit, as in Iguana, or in front of the cloaca! 

 opening, as in Hysteropus. 



We may find (e.g. in the Chameleon) cutaneous structures 

 termed chromatophores, which are little sacs containing 

 pigment of various colours, and each with an aperture which, 

 when open, allows the colour contained to appear, and when 

 closed conceals it. It is by the various contractions of these 

 sacs that the Chameleon effects those changes of colour for 

 which it is celebrated. 



It is in the next lower class, Batrachia, that we find the 

 cutaneous glands carried relatively to their maximum of 

 development. 



They may be aggregated in a mass behind the eye and 

 above the tympanum on each side, forming the so-called 

 " parotoid " glands, as in the common Toad. 



There may be a similar structure on the arms, as in Pelo- 

 bates, or on the upper side of the leg, as in Bnfo Calamita. 

 The whole skin of the back may be of this nature, as in 

 Kalophrynus, or these glands may be localised in two longi- 

 tudinal series, as in Salamandra, where they extend from 

 the head to the end of the tail. Their secretion maybe more 

 or less acrid, as in the last-named genus and in the Toad. 



It is not certain that true cutaneous glands, homologous 

 with those of higher Vertebrates, exist in the class of Fishes. 

 This is remarkable, seeing the very great development they 

 attain in the Batrachian class of Ichthyopsidans. 



Nevertheless, a copious mucus exists on the skin in Fishes, 

 and notably in the Eel. This escapes from the deeper 

 structures through minute orifices, but is by some naturalists 

 considered to be rather itself a modified epidermis than a 

 true cutaneous secretion. 



In most Fishes there is a complex system of special 

 canals, the nature of which has been commonly deemed 

 excretory, but is now considered to be rather sensory in 

 function. These canals are usually disposed symmetrically, 

 and are filled with a clear gelatinous substance. They con- 

 stitute the " lateral line," the passage of which modifies and 

 marks the scales it traverses, and is thus useful in zoological 

 classification the lateral line forming a more or less con- 



