LUCERN ARI^ AND THEIR ALLI ES. 51 



103. Tnfertentacular lobides {Jigs. 54, 56, 60, tx). The render, no doubt, has 

 learned by this time that these bodies are internal prolongations of that part of the 

 parietes of the unibella from which the tentacles take their origin. Their relative 

 position in regard to the latter might well lead a hasty observer to infer their simi- 

 larity to the ampnllaceous sacs of Echinoderraata ; but no very prolonged investi- 

 gation is needed to determine that they have not the form of sacs, and that they 

 are irregular, thick ridg(>s which here and there anastomose into a sort of network 

 (Jig. 56), and send out, from scattered points, more or less flattened, irregularly 

 oval lobular processes. The general trend of the plane of the greater diameter of 

 the latter is parallel with the anterior and posterior parietes of the umbella. The 

 depressions between the ridges of the network are the vestibules of the entrances 

 (^*) to the tentacles ; and tlie lobules, with their ready flexibility, suggest a valvular 

 function which they might perform about these apertures. They consist of only 

 two layers (Jig. 60), the gastrophragma (P) and the chondromyoplax (h'), and 

 neither of these is strictly muscular, although we have elsewhere (^[65, 196) suggested 

 tliat the chondromyoplax is only one undeveloped portion of the muscular layer 

 (opsomyoplax). That would seem to be true here, if we may judge from the irri- 

 tability and activity of these bodies ; or it is possible that the gastrophragma is 

 underlaid by an excessively thin muscular stratum which has escaped our eyes. 

 The surface wall, or gdsfrojJiragnia (P), has the same dimensions as in the more 

 open areas of the general cavity, but is particularly characterized here by the 

 dense deposit of pigment matter over its surface. Tliis accounts for the dark patch 

 of color so noticeable at the proximal bases of the tentacular groups, and whicli 

 remind one of eye-spots, as the body is viewed from in front. The cJioml rom ijoplax 

 (//) is an actual thickening of the mass with wliicli it is continuous, and not a 

 lateral projection from it ; so that the length of a lobule is the measure of the depth 

 of this layer. This is proved by the course of the fibrillar, which pass in direct 

 lines from the distal surface — IvinjT between the bases of the tentacles — to the 

 innermost free ends of the lobules. 



§ 13. The marginal adhesive hodica {CoUetoci/stophora),jigs. 17, 22, 23. 24, 25, 37, 



45, 47 ; a to a**. 



104. Form and. Po!^ifion. — The most attentive examination of an anchor in its 

 extreme old age would not lead one to suspect that it was once a mere tentacle in 

 form, proportions, and general structure. The proofs that this is so may be found 

 in abundance in the section on Embryology (Chapter VI). We only wish, here, 

 to diaw the parallelism for the sake of their homological relations to the regions 

 of the umbella when compared with the tentacles. There are eiglit of these bodies 

 attached singly {Jigs. 17, 22, 37, a) to the eight intertentaculiferous margins of 

 the umbella, exactly half way between the angles (\J,*) of the octagon. Those four 

 which lie opposite the partitions of the umbella are slightly longer tlian the other 

 four, and the average length is about equal to the diameter of the peduncle. They 

 consist of a short, thick stem (Jigs. 23, 24, a'), or neck, supporting a heavy, flat- 

 tened, ovate mass (a*). The neck is attached to one of tlie flattened sides, and 



