41 8 TEGUMENTARY ORGANS 



continuous with the so-called " pith " in the quill of a fully formed 

 feather. The mode of development of these rootsheaths is identical 

 with that of those in the hair, and therefore requires no further 

 elucidation here. 



Teguinentary glands. — The other conversionary productions of the 

 ecderon which we have to consider, are the glandular appendages, 

 which are always diverticula of the cellular ecderon inwards. ^ Under 

 this head I include only those small glandular organs, which, so far 

 as we know, have no reference to any other functions than that of 

 cutaneous transpiration or fatty secretion, referring to the articles on 

 special divisions of the animal kingdom for an account of those organs,, 

 such as the " water-vessels " of Echinoderms and Trematoda, the 

 nidamental glands of Molluscs, the genital glands of Vertebrata and 

 Insecta, which might strictly be regarded as productions of the 

 integument. 



Tegumentary glands in this limited sense are somewhat rare 

 among the Invertebrata. They have, however, been observed in the 

 Annelids, where they consist of delicate tubes, terminating internally 

 by a blind extremity containing a single nucleated cell. Such glands 

 exist on the ventral surface of the head and foot discs in Piscicola 

 and are scattered all over the body in Clepsine and Nephelis. Similar 

 glands are found opening upon the ventral surface of Argulus foliaceus^ 



Simple ccecal glands are scattered over the whole surface of the 

 body of the Procession Caterpillars, opening at the points of the hairs ; 

 on the sides of the body in Myriapods, on the joints of the legs in 

 Beetles and Bugs. 



In Mollusca a peculiar, probably glandular, canal exists in the 

 foot of certain Lamellibranchs, and glandular coeca have been ob- 

 served in the lower surface of the foot in Paludina. A ciliated 

 canal runs in the foot of Pulmonata, and receives glands on each side. 

 The existence of cutaneous glands in the Cephalopods appears 

 doubtful — at least, H. Miiller could only find them as shell glands in 

 the expanded arms of Argonauta. 



Among the Vertebrata, Fishes, Ophidia, Chelonia and Birds,, 

 appear to possess no proper cutaneous glands ^ ; in Sauria they attain 



^ Unless, indeed, these simple " mucous cells," described by Clark and Leydig in Fishe.';,^ 

 and which are merely modified cells of the cellular ecderon, should be regarded as glands. 



^ Dr. Clark, in his excellent account of the skin of the eel (Trans. Mic. Soc. 1849), 

 describes cutaneous glands in that animal. The so-called "glands" of the lateral line, 

 however, have since been shown by Leydig to have a very different structure ; and I confess. 

 I have not been able to convince myself of the existence of the other glands described by Dr. 

 Clark. I can find nothing like them, except the strong perpendicular semi-elastic bands,, 

 which traverse and unite the bundles of connective tissue in this as in other fishes. 



