554 PROCEEDINGS OF THE AMERICAN ACADEMY. 



lining the body-cavity ; then in the body-cavity the four partial dia- 

 phragms ; and finally that part of the proboscis which has not been everted. 

 This consists of nearly the same kinds of layers arranged in the reverse 

 order, namely a peritoneum, circular muscles, longitudinal muscles, nerves, 

 connective tissue, and cuticula. 



The epithelial layer directly beneath the cuticula is not mentioned as 

 such by Ehlers. Since it apparently undergoes an interesting metamor- 

 phosis, it is worthy of further study. 



From the underlying connective-tissue layer eighteen projections of 

 connective tissue pass radially inward between the eighteen longitudinal 

 muscles to the region of the circular muscles. Where the radial projec- 

 tions are continuous with the outer circular portion of the connective 

 tissue the eighteen longitudinal nerves (n. Ig.) are seen cut crosswise. 

 (Compare PI. 2, Fig. 10.) 



Concerning the structure of these longitudinal nerves I have nothing 

 to add to what Ehlers ('64-68, p. 696) has already pointed out. They 

 are evidently surrounded by a protecting connective tissue, within which 

 lie what are apparently nerve fibres. In preparations fixed in vom 

 Rath's picric-osmic-platinic chloride-acetic mixture, the nervous plasm 

 is flocculent and has shrunken away from the nerve sheath. 



From these longitudinal nerves, fibres pass out (PI. 2, Fig. 10) to 

 form the peripheral nerve plexus, which is embedded in the connec- 

 tive tissue occupying the space between the longitudinal muscles and 

 the cuticula. Other nerve fibres (n. r.) starting from the plexus pass 

 radially inward, skirting the longitudinal muscle (Fig. 10); yet appar- 

 ently they do not innervate the muscles, for I have seen no nerve fibre 

 pass through the sheath enclosing the muscle. Still other radial nerve 

 fibres (n. ?'.') can be followed from the longitudinal nerves passing through 

 the middle of the radial connective-tissue projections toward the centre 

 of the sections as far as to the membrane immediately superficial to the 

 circular muscles (PI. 1, Fig. 2 ; PI. 2, Fig. 10). In the anterior region, 

 where the four partial diaphragms, the " Lappen " of Ehlers, are at- 

 tached to the wall of the proboscis, radial nerve fibres occupying the 

 same relative position as those marked in other regions n. r! can be 

 traced into these four pendent structures. Ehlers says concerning these 

 " Lappen " (p. 686) : " By means of a fold it [the fascia wdiich invests 

 the surface of all these parts] forms the four ' Lappen,' which are 

 attached at the boundary between ' Riisselrohre ' and ' Kiefertrager ; ' 

 these ' Lappen ' therefore possess the fine tense membrane on both sur- 

 faces ; between lies a fibrous tissue, which is apparently identical with 



