A characteristic feature of glandular activity is the production of a slight electrical disturbance. In the case of _Malopterurus_ this elsewhere subsidiary function of the skin has become so exaggerated as to lead to the conversion of the skin of each side of the body into a powerful electrical organ.[3] Each of these consists of some two million small chambers, each containing an electric disk and all deriving their nerve supply from the branches of a single enormous axis cylinder. This takes its origin from a gigantic ganglion cell situated latero-dorsally in the spinal cord between the levels of the first and second spinal nerves. _Cement Organs._--The larvae of certain Teleostomes and Dipnoans possess special glandular organs in the head region for the secretion of a sticky cement by which the young fish is able to attach itself to water-plants or other objects. As a rule these are ectodermal in origin; e.g. in _Lepidosiren_ and _Protopterus_[4] the crescentic cement organ lying ventrally behind the mouth consists of a glandular thickening of the deep layer of the ectoderm. In young ganoid fishes preoral cement organs occur. In Crossopterygians there is one cup-shaped structure on each side immediately in front of the mouth. Here the glandular epithelium is endodermal, developed[5] as an outgrowth from the wall of the alimentary canal, closely resembling a gill pouch. In _Amia_[6] the same appears to be the case. In a few Teleosts similar organs occur, e.g. _Sarcodaces_, _Hyperopisus_,[7] where so far as is known they are ectodermal. _Photogenic Organs._--The slimy secretion produced by the epidermal glands of fishes contains in some cases substances which apparently readily undergo a slow process of oxidation, giving out light of low wave-length in the process and so giving rise to a phosphorescent appearance. In many deep-sea fishes this property of producing light-emitting secretion has undergone great development, leading to the existence of definite photogenic organs. These vary much in character, and much remains to be done in working out their minute structure. Good examples are seen in the Teleostean family _Scopelidae_, where they form brightly shining eye-like spots scattered about the surface of the body, especially towards the ventral side. [Illustration: From _Trans. Zool. Soc. of London_. FIG. 6.--Larva of Polypterus. (After Budgett.)] [Illustration: From _Phil. Transactions, Royal Society of London_. FIG. 7.--Thirty Days' Larval Lepidosiren. (After Graham Kerr.)]