g^ LUCERiNAlU^ AND THEIR ALLIES. 



expose the internal base of the organ in question. Then one may either look 

 directly into the passage way, or, if there be any suspicion that it is closed by a 

 transparent membrane, the head of a fine needle can be thrust into it. We have 

 fully satisfied ourselves, by all of these methods, tliat there is here a direct, smooth, 

 and widely open passage leading into the cavity, and that the latter is not sub- 

 divided in any way, but is tolerably uniform in its length and breadth. In the stem 

 the passage has rather the character of a channel, and expands quite rapidly into 

 a tolerably wide chamber {Ji(j. 47, aO soon after it enters the ovate mass. The 

 chamber occupies the middle third of the shorter diameter of the mass, and lies at 

 about an equal distance from the extt>rnal surface both at its sides and at its distal 

 end, yet approxinuites rather more closely to the anterior face. 



109. The walls of the anchors (Jig. 47) are remarkable for their great thickness 

 at nearly all points ; and if there is any exception to this it is to be found in the 

 region which is homologous to the thickest part of the tentacles. Tlie process of 

 development is just the reverse in the two organs ; in the tentacles the wliole ten- 

 dency is to give the nematocystigerous tip a preponderance in point of size and in 

 the thickness of its walls ; whereas, in the anchors, the greater weight is thrown 

 into the midrcgion of the shaft, both in reference to its general amplitude and the 

 incrassation of the walls, whilst the nematocystigerous tip (a^) is gradually reduced 

 to comparative insignificance, a mere reminiscence of its type. It is remarkable 

 that we should liave in tliese organs a repetition of that singular irregularity in the 

 thickness of the walls which is so promftient in and about the adhesive disk at the 

 caudal end of the body. Here, as tliere, the peculiarity is confined to the two 

 innermost layers. 



110. The onier icall {fig. .47, n^) is a direct continuation of the opsophragma of 

 the umbella, but is much deeper than the latter over the greater part of the stem 

 and ovate mass. Oh the anterior face of the stem there is very little, if any, 

 diff'erence, but upon passing around toward the posterior face, and outward also 

 into the ovate mass, the wall thickens rapidly to triple, quadruple, and even sex- 

 tuple the measure in the first place mentioned. There is considerable variation in 

 thickness at diverse points, but it is quite systematic in this respect. Along the 

 broad median furrow it is thinner than anywhere else on the ovate mass, not being 

 more than two and a half to three times the depth on the stem, and even this pro- 

 portion is lessened greatly in the semi-transparent area at its distal end, until it 

 actually falls below what obtains on the umbella. In the remnant of the nemato- 

 cystigerous tip (a-) of the tentacle the wall rapidly thickens again to equal the 

 greatest measurement along the proximal end of the furrow. Passing laterally, 

 from the midline, around the mass, the depth increases gradually until it reaches 

 the maximum, sextuple measurement mentioned above. Where the anterior and 

 posterior parietes of the umbella meet, at the distal side of the base of the anchor, 

 the outer wall thins abruptly just as it joins the ectophragma (»/. 63). The adhe- 

 sive vesicles (coUefoci/.'^ts) which form the main characteristic of the functions of the 

 anchor, notwithstanding their multitude, have nothing to do with increasing the 

 thickness of the wall ; they are merely superficial adjuncts to its mass, while the 



