48 



LUCERNARIvE AND THEIR ALLIES 



tlip opsomyoplax (64), the chondrorayoplax (65), and tlie gastrophragma (75). 

 AUlioiio-li "the dittereuces between the same walls in the tentacles and in the nm- 

 bella are iu certain points very great, the change from the one to the other is by 

 no means abrnpt, as may be seen while we enumerate and describe them, each in 

 its turn passing from without inward. It would be well to bear in mind, during 

 this description, that the tentacles are fully extended. 



97. Tlie upsophraijnia is the foundation of the outer wall {figs. 54, 90, 91, ?i') 

 of the tentacles, and so far as the latter is confined to the shaft it has about the 

 same thickness, excepting at its distal end, where it is sliglitly incrassated and 

 forms the neck-like junction with the spheroidal tip. To complete its course, 

 though, it enters the globose mass {fig. 54, <^^), in fact it almost becomes the mass 

 itself, since it forms so great a proportion of it ; and yet it consists of but a single 

 stratum of cells. Tiiis is effected by a very abrupt and encrmous thickening of 

 the layer, so great, indeed, as to equal fully one-third of the diameter of the sphe- 

 roid. This leaves, then, only a central third to be occupied by the other walls and 

 the cavity of the organ (see also fig. 48, ^^, m'). The thickening {fig. 35, oc^) of 

 the wall at certain points on the shaft, which is to be met Avith now and then, 

 altliougli quite rarely, is not of the same character as in the globose tip, but is a 

 tendency to carry out what is so fully expressed in a normal way in the anchors 

 (^ 166, etc.). But more of this when we come to the description of the latter. 

 There are no adhesive vesicles in the tentacles. We have already spoken of the 

 apparently furrowed and ribbed appearance of the shaft (^f 94), and referred it to the 

 lumen of the underlying bundles of muscular fibres. At times the phenomenon 

 is really on the surface of the outer wall, or within its thickness, and is produced 

 by the peculiar action of these fibres, or at least it seems to be so, for along their 

 course the cells of the wall in question are arranged in lines, and, moreover, they 

 are elongated in that direction. It can scarcely be denied that the muscles are at 

 the bottom of this singular feature, and also that they cause the wrinklings in lines 

 running in the same course (see ^ 202, A). 



98. The teniacvlar mv^sdes are not only the most important element of the pre- 

 hensile organs, but also the most conspicuous. As we have seen above, they lend 

 largely to the pliysiognomical character of the shaft. We speak of this motor 

 apparatus as muscles, and not as a layer, and we do this advisedly, for the fibres 

 do not form a continuous stratum, but the latter is, as it were, split into strips or 

 threads (see % 86), and these are grouped into bundles {figs. 90, 91, m') of two, three, 

 or four. And again we notice that these fibrillae do not lie in one horizon but are 

 more or less superposed, and even mutually intertwined, thus warranting us in 

 using the term fibres for their combined forces. Still there are here and there 

 traces of a tendency to form a continuous layer, judging from the manner in which 

 a fibrilla wanders now and then across the interval from one fibre to another. On 

 the whole, the fibrous bundles run from the base to the tip of the shaft in parallel 

 lines, and are so evident to the senses that they can be counted very readily. By 

 a careful handling of these irritable creatures, taking the precaution not to disturb 

 them by any sudden movement, but always slowly and steadily, and with no little 

 patience, turning them from side to side, or even over and over", we have succeeded 



