15 



On the Potion Gland in the Jaw of Geophilus longicornti. 

 By Thomas P. Wright, Esq., M.D., &c. 



At a Meeting of the Cotteswolds Naturalists' Club, held at Rodborough 

 Common, May 18th, 1847, Dr. Wright, of Cheltenham, exhibited a beautiful 

 preparation of the Geophilus longicornti , Leach, in which he had observed 

 the veneniferous glands of that Myriapod. He had found no description of 

 these glands in any of the great authorities on the structure of the articulate 

 animals whom he had consulted, from which he inferred that these bodies 

 had hitherto escaped observation. 



Dr. Wright observed that the salivary glands in the vertebrate animals 

 are in general absent in those classes and tribes which live habitually in 

 water. In Fishes they are absent, an increased mucous secretion being 

 poured into the mouth by a great development of the buccal follicles. In 

 Batrachia distinct glands are absent, a compensative secretion being 

 supplied by the mucous glands of the mouth and tongue. In the Cetacea 

 they exist only in a rudimentary state. Hence the conclusion that animals 

 that seize their prey in the water, and swallow it without mastication, have 

 no necessity for saliva as a preliminary solvent for the digestive process, the 

 gastric juice in these animals being sufficient to complete the chemical 

 changes in the stomach. In the invertebrate classes salivary glands are 

 absent in all the Radiata, nor do we observe these bodies in the Tunicated 

 or Acephalous Mollusca ; but they are found in the Gasteropoda and 

 Cephalopoda ; they are absent in the Entozoa, but exist in a rudimental 

 state in the Annelida and Crustacea. In all the classes of the Articulata 

 that respire air, as Myriapoda, Insecta, and Arachnida, salivary vessels can 

 be demonstrated : these organs may be subdivided into simple and com- 

 pound glands. 



A. When the secretion supplied is a fluid concerned in the digestive 

 process, the secreting organ is a simple tube with its distal extremity closed. 



B. When the secretion supplied is used for the destruction of prey, the 

 secreting organ is a compound body or gland. 



In the major ity of Insecta the salivary vessels are simple ramified tubes 

 that open into the gullet, but in Hemiptera simple tubes and glandular 

 bodies coexist ; the former I regard as the true salivary organs, the latter as 

 veneniferous glands for the destruction of prey. In Nepa, Notonecta, 

 Naucorti, and Ranatra these bodies are beautifully developed. 



In pulmonary Arachnida the veneniferous glands are situated in the 

 cephalothorax ; their excretory ducts arise from the anterior part of the 

 gland and traverse a minute canal in the mandibles, and open at the 

 perforated extremity of these organs. 



In Myriapoda, as in the preparation of Geophilus longicornti now before 

 us, the veneniferous glands he at the base of the mandibles among the 

 striped or voluntary muscles that occupy this region. With an inch glass 



