LUCERNAllI.E AND THEIR ALLIES. 95 



rim like a network in the interspaces. Frequently higlily refracting, large, oval, 

 or globular bodies (/) may be observed, mixed with the coarser pigment, at the junc- 

 tion of three or four cells. A close examination proves these to be urticating vesi- 

 cles (nematocyffifi). Their refracting power renders them cpiite brilliant objects, 

 and lights up the face of the wall with bright, salient points. The bristle-like pro- 

 jections, which arc often observed on the free surface of the wall, are portions of 

 the blastema which are apparently tlirust outward by the partially extruded fila- 

 ments of the nematocysts. More will be said of this hereafter, in the description 

 of these offensive weapons (§ 30), and the true relation of the bristle-like bodies 

 will be amply explained. (See also ^[ 203 (A) ). 



194. J7te ectopliragma (^f 03) of the umbella and peduncle {fuj. 87) consists of 

 cellular elements which exhibit a close affinity Avith those of the opsophragrna 

 (*\ 193), still there is a decided and readily observable difference between the two. 

 The cell-membrane, the exterior and interior configuration of the cells, their size 

 and proportion, their mode of arrangement, the fluid-like contents, and, finally, the 

 granular interstitial blastema, might all be described in the same words as used for 

 the components of the opsophragma. The main diversity then is narrowed down 

 to the character of the nvdcu>^ {<P), and this we shall find is not inconsiderable. 

 Strictly speaking, the nucleus is no longer visible, if it exists at all, and seems to 

 be either covered up, or replaced by very dark, highly refracting, irregular, large 

 granules, which are heaped together in twos, threes, or fours and fives at the side 

 of tlie cell. Occasionally they are deiached and lie in the midst of the homoge- 

 neous contents. These psexulo-nudei are many times larger than the nuclei of the 

 cells of the opsophragma, and such is their opacity and intensity of color, to say 

 nothing of size, that they eft'ect far more, in producing the tint of this stratum, 

 than the interstitial, granular blastema {(■). Hence it is that this face of the 

 umbella is darker than on its front. We should add, also, that the nematocysts (/) 

 are more numerous than at any other part of the exterior of the umbella, and fre- 

 quently are collected in groups of from three or four to a dozen, glittering, from 

 their strong refraction, like clusters of jewels. 



195. The op.<fomyopJax (*\ 64) of the umbella {fig. 85, m). In the general 

 description of this layer we have stated that it uniformly spreads beneath the 

 opsophragma, and that it is made up of fibrillse which are placed side by side. 

 We premise this much here in order that we may also recall the arrangement 

 of similar fibrillie in the tentacles, in which they are disposed, in a brok(>n 

 stratum, at regular distances apart, in groups or bundles. These are the main 

 differences of the muscular system in the two regions in question, and therefore 

 the description of the histological elements of the one may serve for that of 

 the other. Inasmuch, however, as we have illustrated the microscopic structure 

 of this layer in the tentacles with such fulness of detail, and under more advanta- 

 geous circumstances than could be had elsewhere, we shall rc^er the reader to the 

 dcscripti(m of tlie histology of those organs for whatever information may be 

 desirable in regard to the composition of the fibrilla;. The cellulo-fibrous elements 

 are alike in both. We refer also to paragrajih 199 for a description of the still 

 more higlily developed muscles of the peduncle. 



