ORGANS OF SECRETION. 



like the periodical cuticular separations of most vertebrata. 

 Some as pennatula, when excited, emit a bright luminosity, 

 which is secreted by the individual polypi. These luminous 

 secretions, so common in the radiated and the molluscous 

 classes, appear to accompany the mucous secretions of the 

 skin, or of the alimentary canal. Numerous zoophytes 

 secrete from their surface large quantities of calcareous 

 matter, mixed with a coagulating muco-gelatinous substance 

 to form the solid extravascular skeleton of lithophytes, and 

 others pour out upon their surface, or into their interior, a 

 soft homogeneous coagulable matter, which soon hardens to 

 constitute the flexible sheath or the axis of keratophytes. 

 Many secrete colouring matters of various and vivid hues, 

 sometimes along with the earthy matter of the skeleton, as 

 the purple of corallium, tubipora, melitcea, and sometimes 

 without it, as in the deep hues of actinia, zoanthi, pennatula. 

 The interior of the stomach of many zoophytes, as actinia, 

 produces a copious secretion which appears to prove quickly 

 fatal to, and quickly to dissolve their victims when seized and 

 swallowed alive, and these parts of the stomach appear striated 

 with thick opaque patches, like a blastema of future follicles. 

 This condition of the secreting surface of the stomach, is more 

 follicular in appearance in many sertularite, where it is reduced 

 to minute aggregated coloured spots, like rudimentary biliary 

 tubuli filled with their coloured secretion ; and from the sto- 

 mach of the polypi ufflustrce, a distinct hollow follicle extends, 

 forming an arrested development of a liver. We may regard, 

 however, most of the glandular or secreting organs of these 

 lowest classes, as still in their simplest condition of flat 

 smooth secreting membranes, which have not yet developed 

 even cryptee or follicles to extend their surface, and to pro- 

 vide for the different kinds of products, and yet their secret- 

 ing powers are often very considerable, and their products 

 most varied. They present no distinct glandular structures 

 for elaborating those very different materials from the food 

 which they take in. Each species developes its gemmules 

 always from determinate points of the body, and not indis- 

 criminately from every part of the fleshy substance. We 

 may consider, therefore, that even the ovariuni, or the gland 

 for secreting ova which is developed in higher classes of 

 animals., presents itself here in a rudimentary state, as a 



