116 



LUCERNARI.E AND THEIR ALLIES. 



§ 29. nistohinj of the DUjitnli (^ 52, 116-121) {figs. 98, 99, 100, 101, 102). 



213. Topography. — In the general description of the walls (^ 116-121) of the 

 (lio-itiform bodies we have, unavoidably, entered so far into the consideration of 

 their histological elements that there is but little to add here. The disposition 

 of these elements, whether they be true cells or fibre-like in character, is so 

 thoroughly intermingled with the topographical apportioning of the several layers 

 and their subdivisions, that any attempt to describe the latter without including the 

 former would utterly fail to present a picture of the nature of these organs, beyond 

 a mere idea of their outlines. We will not, however, repeat here what has already 

 been given so fully, but beg our readers to consider § 15 and the present section as 

 one, for the time being. In regard to a single point in the paragraph (^f 117) which 

 concerns the relative positions of the nematocysts and the colletocysts on the sup- 

 posed flat sides of the lUgituU, we would add one more fact, without commenting 

 upon its significance, if there be any. We refer to the corresponding position of 

 the vibratile cilia {figs. 98, 100, co) with those on the genital organs, the areas of 

 both facing in the same direction in a general way; Avhilst the area of the colle- 

 tocysts (a) corresponds to that in the genitalia which bears the layer of reproduc- 

 tive bodies, either eggs or spermatozoa. 



214. Gastrophragma of the DigitiiU (i"). — Within the area which is covered by 

 the colletocysts (a) the latter occupy about four-fifths of the space, and the true 

 cells the rest, filling up the intervals ; while, on the other side, the nematocysts 

 (/) are set quite wide apart, and are a subordinate feature in the composition 

 of the layer. In a profile, sectional view {figs. 99, 100, a) of the wall in which 

 the colletocysts are imbedded, the latter appear to constitute the whole layer, so 

 nc^arly obscured are the cells by these densely packed vesicles ; yet, from a face- 

 view {fig. 99, \a,fig. 101), we learn that the cells do actually form a continuous 

 stratum, but so thoroughly intersected by the vesicles that it has the appearance 

 of a network of a single, or more or less double, row of cells. 



Whether on the side of the nematocysts, or where the colletocysts prevail, the 

 cells of the gastrophragma(/r/. 101, i') have the same structure and contents. They 

 are by far the smallest of those that belong to this layer in any part of the body, 

 but they have the same elements. There is the same clear homogeneous contents, 

 and a like single nucleus, so encrusted by pigment-matter that the mass occupies 

 from one-third to one-half the diameter of the cell. It is a notable fact that none 

 of these cells underlie the colletocysts, as they do in the ectophragma of the colle- 

 tocystophores (^ 208 (A)), and for this reason, that the colletocysts of the ,Ugi- 

 tidi extend through the whole depth of the gastrophragma, and abut immediately 

 agamst the muscular layer; and in a measure adhere to it. In regard to the 

 latter statement, we will say, in passing, that the colletocysts are the last to break 

 away from the underlying tissue when the layer is disorganized by the application 

 of fresh water {fig. 103, o) ; and they seem to be organically attached by a nar- 

 row, short stem or neck to the muscular layer (o). In point of size they are quite 

 dunniutive, not more than one-quarter tlie diameter of those in the collctocysto- 

 phore {fig. 97, «), and yet about three times the diameter of those in the pcdun- 



