Structure of Mngelona. 429 



iuferior margiu of tlie central muscular area, and sends a 

 bar to meet its fellow of the opposite side. The ohitinous 

 supports of the vascular area and the septa betweeu the 

 muscular spaces are stro)ig. Lastly, the median muscular 

 investment disappears^ leavings about the origin of the 

 tentacles, only the external chamber, which sends a process 

 outward to the base of the tentacle, and another from the 

 same point to join the ventral cuticle ; while between these 

 lie the hypodermic nerve-area and the neural canal (supe- 

 riorly and externally). The chitinous investment does not 

 closely surround the external muscle, but, sending its low^er 

 bar upward and inward, a considerable space is by-and-by 

 formed. Thereafter the chitinous layer is continued back- 

 ward as the external support of the muscle, and may for the 

 present be left. 



The chitinous basement-system thus constitutes a kind of 

 endo skeleton for the entire snout, giving, with the cuticle, 

 tirniness to the organ in its ceaseless thrusts into the sand, 

 supporting its muscles, and confining their action (in lieu of 

 a circular coat) to the most favourable lines, and with its 

 flexible plates — even more than the beams of a ship — lending 

 the necessary power of resistance to the yielding tissues of 

 the snout and protecting the blood-vessels. Moreover, the 

 continuity between the base of the tentacles and the chitinous 

 support of the ventral longitudinal muscles gives a com- 

 pleteness to the system which most admirably adiipts the 

 whole anterior region for its special functions. 



It is found — to continue the account of the median longi- 

 tudinal muscles — that they are not simple bands, but, as 

 might be inferred from their chitinous investment and the 

 arrangement of the fibres, they act to a certain extent 

 obliquely as well as longitudinally. Before the appearance 

 of the lateral muscles at the tip of the snout, and when the 

 spectacle-like arrangement of the pair exists in transverse 

 section, each consists of a thick dorsal arch of fibres, wliich 

 proceeds a short distance downward at each end, while the 

 ventral part of the chamber is occupied by granular tissue. 

 The muscular fasciculi are nearly linear and slant from 

 above downward, with varying degrees of obliquity according 

 to the condition of the preparation. When the spaces 

 assume the form of a crown, fasciculi pass from the arch 

 nearly at right angles; others extend from the upper part 

 of the median septum do\^nward and inward. Moreover, 

 the outer fasciculi from the external septum join the larj^er 

 which pass to the bottom, then curve inward along the 

 ventral chitinous floor, and meet the descending fasciculi at 



