MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 131 



into its posterior half, and that it communicates dorsally with a broad transverse fissure near the 

 dorsal side of the organ. (Figs. '•> and 10, H.) The transverse horizontal fissure extends almost 

 to tlir posterior end of the organ. 



The anterior free portion of the organ is firm in texture and is seen to be partly divided into 

 Lobes by fissures extending from the edges of the vertical fissure. In longitudinal and cross 

 sections of the organ the deeper parts of the longitudinal fissure are seen to he bordered by 

 thin, shelf-like laminae, which extend about halfway to the lateral edges of the organ. (Figs. 10 

 and t'.ii. ) The laminae do not reach the posterior part of the organ, extending only as far as the 

 posterior end of the vertical fissure, which ends in a line directed upward and backward. 



The regions posterior to the lamina? and dorsal and lateral to the horizontal fissure are 

 glandular. The openings of the glands can be seen with the naked eye or a hand lens upon the 

 \\:ills of the horizontal fissure. The glandular part of the organ is quite, distinctly different 

 from the remainder in appearance and texture, but still is firm and hard. 



Both the lobules of the anterior region and the horizontal lamina? radiate from a small region 

 of firmer tissue near the anterior end and on each side of the vertical fissure. (Fig. 9.) The lobules 

 noticed at the sides of the anterior portion of the vertical fissure are thick and fleshy and often 

 have their edges rounded. Posteriorly they are seen to graduate into the horizontal lamina?; as a 

 matter of fact, lobules and lamina 3 are differently developed members of a single series. Counting 

 all as laminae, there are from 20 to 2-t laminae upon each side of the vertical fissure. 



Several muscles are attached along the lateral edges of the anterior part of the organ. At 

 their attachment they usually form a distinct muscular ridge from which two principal muscles 

 separate themselves on each side. One pair of muscles extends backward along the sides of the 

 organ to penetrate the muscular base of the buccal mass above and outside the ventral buccal 

 retractors. (Fig. 8.) The other pair of muscles extends outward and each soon divides into 

 two branches. The anterior branches are spread out upon the bases of the superior labial lobes. 

 The posterior branches go to the sides of the cephalic sheath below the anterior. This arrange- 

 ment of the muscles shows distinct resemblances to that of the muscles of the inferior labial 

 lobe of the female. (Fig. 26. ) 



A large nerve arises from the pedal ganglion just outside the infundibular nerve. (Fig. 41, 

 7 and 35.) The two nerves pass along the sides of the organ of Van der Hoeven, entering it a 

 little anterior to its middle. 



A branch from the tentacular artery of each side supplies Van der Hoeven's organ with 

 blood. These are the same branches which, in the female, supply the inferior labial lobe. (Text- 

 fig. 10, p. 182, 1 and 3.) 



The firm tissue forming so large a proportion of the anterior part of the organ is composed 

 of a thick-meshed reticulum of elastic tissue til ires, in the interspaces of which run bundles of 

 muscle fibres. The tunic is composed of a layer of muscle very distinct from the underlying 

 tissues. The bodies of the lobules and the lamina 1 are almost entirely composed of elastic tissue. 

 The bodies of the thin horizontal laminae which lie hidden within the organ are not thicker, and 

 frequently not as thick as the epithelium of either surface. 



The epithelium of the lobules and the lamina? is of exactly the same character. It averages 

 8U/< in height, and is composed of a single cell layer comprising two entirely different sorts of 

 cells. The more evident, and at first sight the only sort, are slender columnar cells from 5/* to 

 8/* in transverse diameter. Oval nuclei situated in the very liases of the cells make a distinct 

 row along the lamina?. All these cells appear to be able to form a secretion, which is contained 

 in the cells in the shape of granules, which stain with remarkable intensity. But while all the 

 cells appear to possess the power of secretion, not all in my preparations were exercising it. 

 Next to areas in which all the cells were choked with secretion are areas the cells of which con- 

 tained no secretion whatever. And as a rule, there is no gradual transition from one area to 

 the other. The boundaries of the areas are distinct; upon one side all the cells are crowded 

 with secretion, upon the other side not a single cell contains any secretion. In only a few places 

 are secreting cells mixed with others not secreting along the edges of the areas. As a rule, the 

 areas free from secretion are near the edges of the lamina? turned toward the fissure (the 

 Vol. 8— No. 5 3 



