MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



125 



A 



sheath. In the thicker portions the amount of muscle tissue within the dermis is very considerable, 

 and is roughly arranged in the longitudinal and circular layers already mentioned. It must not 

 be forgotten that a quite considerable portion of the 

 sheath is derived from the tissues of the second and 

 third tentacles after these have become continuous with 

 the tissues of the former. The spaces between the mus- 

 cles are occupied by fibrous and elastic connective tissue. 

 The sheath is penetrated by a perfect network of vascu- 

 lar lacuna?. 



Until we have some idea of the function of the 

 glandular area upon the outer side of the spadix sheath 

 the term •"slime gland" will do very well to designate it. 

 It is surprising- that this structure should not have been 

 mentioned by Yayssiere in his excellent paper upon 

 Nautilus. The slime gland forms a nearly circular area 

 upon the outer side of the spadix sheath, from 25 to 

 30 millimeters in diameter, and is considerably raised 

 above the surrounding surface, besides being of a much 

 darker color, all in all being a quite conspicuous organ. 

 (Fig. 14.) Numerous pores, the openings of the glands 

 within, open upon its surface. The glands are formed 

 of long, branching tubes, which are packed closely 

 together, and occupy three-quarters of the thickness 

 of the sheath at this point. (Fig. 57.) The sheath 

 contains but little muscle tissue in this region, being 

 composed almost entirely of fibrous connective tissue 

 which, below the slime gland, is reduced to a network 

 inclosing great numbers of vascular lacuna; of all sizes. 

 The larger spaces have endothelial walls. The lacuna? 

 are much more numerous than they are represented in 

 Fig. 57, by far the greater number being too small to 

 be shown in such a figure. 



The structure of the glands is quite simple. From 

 a short, narrow neck arise several tubular outgrowths. 

 (Fig. 57; Text-tig. 6, A.) Most of these are long and 

 slender and extend into the sheath nearly at right angles 

 to its surface. Around the outer part of the neck are 

 often grouped short tubules or mere outpocketings of the 

 wall. The main tubules may themselves be branched. 

 The tubules of each gland lie parallel and close to each 

 other, separated by only a small amount of submucous 

 tissue. (Text-tig. 6, A and B.) The tubules are packed 

 together so that they form a package of almost equal 

 transverse diameters from end to end. 



The tubules are lined by a single layer of tall, col- 

 umnar secretory cells. The lumens of the tubules are ex- 

 tremely narrow, being rarely of greater width than half 

 the height of the cells lining them. (Fig. 57.) The 

 epithelial cells are extremely slender, averaging about 

 100/* in length and i/.t to 8m in their transverse diameters. 

 (Fig. 57, A.) The epithelium rests upon a thin basement 



membrane. At the very base of each cell is a small oval nucleus, 3/t by 8m in its dimensions. 

 From just above the nucleus to its free end each cell is packed with deeply staining granules of 



Text-fig. 6.— Slightly diagrammatic sections of a siugle 

 gland of the slime gland of the spadix sheath. 

 A, longitudinal section; B, transverse section. 



