80 



LUCERNARIyE AND THEIR ALLIES. 



third, at least, in lateral extent; but no more between the axis and the periphery. 

 At the posterior end {pj. 127) they are still more expanded, indeed almost to 

 double their diameter in front. In a transverse section {fig. VIS) they present a 

 broadly ovate outline, with the narrower end next the axis ; or in the posterior 

 region {fig. 127) they are approximately triangular. 



\m. The Mmcular S//stem {figs. 20, ^i, 127, 128, r).— We have once before 

 spoken of the muscles of the umbella {fig. 20, ^i), and yet revert to them here in 

 order to add that their presence is proved not only by their histological elements, 

 but by the already well pronounced ridge-like incrassations which extend like the 

 rods of a fan from the proboscis to the margin of the umbella. The marginal 

 muscle is still inconspicuous, as far as external appearances would indicate its pres- 

 ence. The chief point of interest is in the peduncular cords. Viewed from with- 

 out they might very naturally be mistaken for a second set of canals alternating 

 with the true camerae. They have, in reality, the form of a hollow cylinder, which 

 is slit open along its whole length on the side facing the axis. In a transverse 

 section {fig. 128, r) they appear like crescents, with the horns nearly in contact, 

 imbedded in the chondrophys (c'). At the posterior end the cylinder expands 

 {fig. 127, r) a little and terminates abruptly, without sending off a process toward 

 the axis, as is done in the later periods of life. The mass seems to be composed 

 of minor cords placed side by side, so as to inclose, in a rough way, a space, which 

 opens on one side, as mentioned above. This gives the muscle a longitudinally 

 furrowed appearance, both without and within the cylinder. The deeper and 

 more conspicuous furrows are evidently the spaces between the minor cords, and 

 the smaller furrows are mere longitudinal depressions in the solid mass. If, now, 

 we contrast these cylinders with the cords of a full grown individual {fig. 52, r), 

 we shall find that the younger ones are proportionally a great deal larger, as any 

 one may see at a glance, upon inspecting the transverse section of the peduncle 

 of the animals at these two extreme ages, and comparing the cords with the 

 camerse (t^). Observe also the space which the former occupy between the latter, 

 or between the axis and the periphery of the peduncle. Finally, we would draw 

 attention to the peculiar relation of the interior of these muscular cylinders to the 

 chondrophys. It would seem to be a law in the organization of these parts that 

 the chondrophi/s sliall form a surface of contact to every exposed part of the mus- 

 cle, and, therefore, here in the young, even the interior face of the contractile 

 cylinders abuts against the fibres of the chondrophys (c^), the latter entering the 

 cavity of the former through its longitudinal slit. These fibres have essentially 

 the same arrangement throughout the peduncle as in the full grown body (^f 198), 

 but they are much fewer, and are less delicate. 



IGOd. The Chondrophys {figs. 127, 128, c').— The great thickness of this layer 

 in the peduncle at this period leads us to the conclusion that it was not much less 

 in the previous phase, since in that it was very deep in the umbella. Its relation 

 to the muscular cords has already been indicated with sufficient precision when 

 describing these bodies, except so far as regards its histological, fibrous elements, 

 and these will be treated in due time, in the chapters on the structure and devel- 

 opment of the tissues (Chapter VII). 



