24 



LUCERNARIJ3 AND THEIR ALLIES. 



adherent face of the latter, and meet exactly in the axial line of the body {fi,j. 

 18 y'). The shaft, then, is slightly fonr-lobed in a transverse section {fig. 52), tiie 

 dividing furrows {t") running as if in continuation of the four slight, broad furrows 

 which overlie the partitions in the umbella (45), and therefore standing in the same 

 relation to the vertical and horizontal planes of the longitudinal axis. In the 

 peduncle the furrows overlie the four muscular cords (/•) which intervene between 

 the longitudinal canals (r''). The sides of this shaft run nearly parallel to the axis, 

 diverging but slightly, when the animal is fully expanded, except at the posterior 

 terminus, wliere they spread abruptly to form a disk-like, truncate expansion {fi(js. 

 IT, 37, 60 y). This disk is four-lobed by the indentation of the longitudinal fur- 

 rows, and its posterior face is not only divided into four equal areas by these furrows 

 {fi'J- 18 >')' b"^ i^ traversed in every direction by minor furrows, which form a sort 

 of network. The obvious office of the disk is that of an adherent organ, and to 

 that its minuter structure corresponds, since we find in its broad, transverse face 

 a multitude of adherent vesicles (see §§ 14 and 28), identical Avith those which are 

 imbedded in the surface of tlie marginal bodies (§§ 13 and 27) of the nmbella. 

 The general surface of the peduncle is slightly undulating when fully extended, but 

 upon contraction it becomes quite strongly corrugated, and principally in a trans- 

 verse direction. Under all conditions, whether of extension, expansion, or contrac- 

 tion, its disciform posterior termination retains its peculiar physiognomy, not only 

 in regard to form but in reference to its singularly areolated surface. The flexi- 

 bility of the peduncle has been noticed in an earlier paragraph (35) on the mode 

 of locomotion of this creature. 



55. The sheath, which we have formerly mentioned (32), is so short and trans- 

 parent, and so closely set to the surface of the pedicel, that it is scarcely noticeable. 

 It covers but a short space, reaching from the edge of the adherent disk hardly 

 more than an eiglith of an inch forward. It has sufficient consistency to retain its 

 shape in a great measure after the pedicel has been withdrawn, and, although it is 

 nothing more than a filmy excretion, its presence adds largely to the stock of 

 characters which stamp upon this region of the body the impress of the hydroid 

 morph. 



5(). Tlie caudal interior is much more expressive of the hydra-morph than the 

 exterior, for here we may find special parallelisms in organization with that of the 

 scyphostoma-form of the strobiloids, as described by us in subsequent pages (Part 

 XI). The exterior, by its form and the adherence of its base-like terminus, lends 

 greatly to its similitude to a hydra ; but it is the interior which, by its evidently 

 special, organized fitness to perform the functions of the hydra-morph, gives the 

 strongest testimony in this case. We discover, in the first place, not a single open 

 space in this region, but no less than four interior compartments {fig. 52), and 

 they are what appear from the exterior, to the superficial observer, to be so many 

 dark longitudinal cords {figs. 17, 66, t^), and which obscure, by their semiopacity, 

 the true muscular cords (;•) that lie intermediate to them. 



57. These caudal compartments {r% or longitudinal canals of the peduncle are 

 nothing .more than four diverticnli from the main cavity ; but yet they stand in 

 such peculiar, definite relations to the other main compartments, and with like 



