LUCERNARIJ3 AND THEIR A LLIES. go 



75. The gastrophragma (PI. iii, fig. 33 ; PI. iv, figs. 44, 47, 48 ; PI. y, figs. 53, 

 54, 58, 60; PI. yx, .A>. 61, 62; PI. yii, figs. 74, 77, 82, 83; PI. ym, »."90, 91; 

 PI. IX, figs. 98, 99 ; PI. x, /7f/«. 127, 128, i to i'). — Excepting in the area over which 

 the oomyoplax {gastromyojilax, 74) is spread, the lining wall of the general cavity 

 of the body is applied directly to the inner face of the chondromyoplax (^ 65) and 

 the chondrophys (69), .and follows them through all their divergences into the ten- 

 tacles, anchors, genital saccules, and over tlie digitiform bodies ; and faces every 

 indentation, no matter how deep or narrow, nor how extensively ramified ; not even 

 excepting the jagged, tortuous passage-ways between the cameroe, at the posterior 

 end of the peduncle (72). Since the nutritive fluid circulates within the immediate 

 embraces of tliis layer, we have given it the appellation whicli heads this paragraph ; 

 but lest this might mislead the reader into a misapprehension of our views of its 

 homological relations, it is necessary for us to state here that it is the same as what 

 we have termed the mesophragma in the medusa-cephalid of Hydroida. It does 

 not, however, bear the same special relations to the walls on each side of it that 

 obtains in the Hydroida and Strobiloida, and it is this difference which constitutes 

 one of the most essential grounds of argument in f^xvor of separating the LucernariiE 

 from the other two orders. In the Strobiloida the gastrophragma is a double layer 

 throughout the area over which the chymiferous fluids circulate; the chymiferous 

 tubes, so-called, being merely spaces left where the juxtaposed faces of the anterior 

 and posterior walls separate from each other. In the Hydroida the gastrophragma 

 is a single wall within whose solid mass are hollowed a set of longitudinal and cir- 

 cular channels — the chymiferous tubes. In the Lucernariae neither one nor the 

 other of these modes is prevalent, nor is the gastrophragma uniformly continvious, 

 since it is interrupted at the partitions where the chondromyoplax and chondrophys 

 are brought into actual contact (67). It is always present as a lining Avail — com- 

 posed of a single stratum of cells — where there is a cavity, but in no case does it 

 lie, a solid mass, between these strata. It always has one free surface throughout 

 its length and breadth, whicli cannot be said of the corresponding layer, neither in 

 the Strobiloida nor in the Hydroida. 



76. This layer varies in thickness to a great extent, and is considerably diversified 

 in the functional subdivisions to which it is apportioned. At the edge of the mouth 

 the passage from the opsophragma (^f CA,fig. 53, if) into this layer (;") is rather 

 abrupt, as the latter suddenly thickens so as to exceed the former by about one-tliird 

 in this respect, and retains this depth to the base of the proboscis. There it begins 

 to thin off (f) and gradually diminishes to the dimension of the opsophragma; and, 

 excepting in that part of it which covers the digitiform bodies {figs. 47", 98, j''), it 

 retains this measurement throughout the broader, open chambers of the umbella 

 and the peduncle. Whenever it becomes a part of some organ it changes its 

 character and, usually, its thickness to a greater or less extent. On the genital 

 saccules {figs. 74, 77, i') it is about as thick as in the broad areas about them, but 

 it rapidly increases in depth by one-third as it extends over the digitiform bodies, 

 and even by one-half at the ends {fig. 98, C) of the latter. At the tips of the 

 intertentacular lobules {figs. 54, 60, /') it is as thin as anywhere, but from these 

 points until it fairly enters the cavity of the tentacles it thickens very rapidly and 



