30 



LUCERNARI^ AND THEIR ALLIES. 



latter, the one seeming to bear the same relation to the other that the cells of 

 some tissues do to the cyiohlasfcma in which they arc imbedded. We shall speak 

 of this again in the section (§ 2-3) on histology, and consider it here as a distinct 

 layer, on account of its large share in making up the bulk of this subdivision of 

 the lunbella. 



66. At the edge of the lips of the manuhnnm {fig. 53, p^) the chondromyoplax 

 takes its rise with a sharp border {h'), but rapidly thickens until a section of its 

 diameter measures six or eight times that of the neighboring opsophragma (61). 

 At the base of the proboscis it thins considerably {h), but with varying degrees, 

 according to the direction in which we trace it. If we follow it along the 

 l)r()boscidial buttresses (*. e., from the angles of the manubrium) passing between 

 adjacent genitalia, directly to tlie border of the umbella, but a little to one side of 

 the marginal corpuscle, we shall find that it preserves a tolerably uniform 

 thickness until within a short distance of its periphery, and then it thickens again 

 at a rapid rate and continues to do so {fgs. 61, Q2, h) until it terminates abruptly 

 with a concavo-truncate edge, only separated from the equally abrupt terminal 

 border of the chondrophys (c) by a thin fold {k^) of the opsomyoplax (*\ 54). It is 

 this fold, then, which is the peripheral terminus of the muscular layer of the 

 umbella, and at the same time the intervening partition which prevents the chon- 

 dromyoplax (?)) from abutting directly against the convex edge of the chondrophys 

 (c). Here is the dividing line between the two antero-posterior subdivisions of 

 the umbella, and such, we shall learn, is the characteristic feature of it at all points 

 of the periphery. If we trace the chondromyoplax from the buttresses directly to 

 the anchors, it will be seen that it does not thicken so rapidly as before near the 

 latter, and that it passes directly into them {fig. 4T, ¥), as it cannot otherwise do, 

 since these organs are nothing but saccular protrusions of the marginal portion of 

 the anterior face of the umbella. The mode of termination at the distal side of 

 the base of the anchors is the same as at all other points in the periphery. Within 

 this saccule the chondromyoplax thickens rapidly as it enters, and attains to a 

 greater depth by the time it reaches the muscular partition {k^) which divides it 

 from the chondrophys, and there ends abruptly (against ¥). Again, if we make 

 a section of this layer along one of the genital halves from the proboscis to, and 

 inclusive of, one of the bunches of tentacles {fig. 37), it does not appear to differ 

 ni point of thickness from the last section, but its course is varied by diverging at 

 the digitiform bodies {fg. 98, I') and every genital saccule {figs. 74, 77, U"), and 

 penetrating them to form one of their strata ; and finally, without any change, it 

 passes onward and into the tentacles and becomes a component of no small propor- 

 tions in those organs {figs. 90, 91, ¥). After traversing the intervals between the 

 tentacles, diverging into the latter on the one side {figs. 54, 60, ¥\ and into the 

 intertentacular internal lobules (//') on the other, it terminates at the distal side of 

 the tentacles (against ¥) in the same way as described in the other sections, but 

 with a thickness less by one-half 



67. There are four places in the umbella at which the chondromyoplax comes 

 nito du-ect contact with the chondrophys, and these correspond to the four lines 

 along which the anterior and posterior internal faces are united to form the parti- 



