L U C E 11 N A III ^ AND THEIR ALLIES. 25 



precise relations to the several members of the organization, that they are by no 

 means to be touched upon slightly in this general sketch. They lie exactly in 

 the same relation to the vertical and horizontal axial planes as do the four anterior 

 umbellar compartments {fig. 37, -v]-'), and, as mentioned above (53), alternating 

 Avith the four muscles (/•) of the pedicel, whicli run continuously backward from, 

 and in the same trend with, the partitions of the umbella (sec figs. 37 and 50, t^^ 

 to r'-). They are narrowest at tlieir entrances (t^), and do not increase in diameter 

 for a short distance, but soon they broaden rather abruptly, and then gradually 

 widen as we follow them backwards initil they reach the transverse wall of the 

 disk-like, adherent organ (figfi. 37, 51, y), where tlicy again broaden rapidly, and 

 become continuous (r") witli one another through lateral channels, and occupy 

 nearly the whole thickness of the peduncle. In a longitudinal section (figs. 37, 

 50, 51) their outlines appear quite ragged, and this irregularity seems to increase 

 toward the posterior end, and finally the indentations become so deep as to meet 

 (t"^) each other between adjoining canals, and form thereby very tortuous inter- 

 communications in the solid gclatiniform mass. Upon making a transverse section 

 (fig. 52) of the peduncle, the outline of these canals has an ovate figure (r^), 

 with the narrower ends nearest the axis of tlie body, and the broader next the 

 periphery. The vertical and horizontal axial planes correspond, therefore, to the 

 larger axis of these ovate figures. Their broader ends, that is the distal sides of 

 the tubes, lie about as far from the surface of the pedicel as tlieir narrower ends 

 are from the axis, leaving about the latter a solid mass, which is between one- 

 fourth and one-third the diameter of the whole caudal region. Between every two 

 tubes there is a little more than twice as much space, filled by solid matter, as each 

 one of them occupies. The dark color of these tubes is owing to the large opaque 

 muscles of the cells of the lining wall. 



58. The solid gelatiniform mass of the pedicel, which is mentioned above (57), 

 is directly continuous with an identical substance (fig. 50, c' to <■■) wliich consti- 

 tutes the bulk of the wall of the posterior face of the umbella, and gives to it that 

 resilient consistency so characteristic of it v/hen contrasted with the anterior face. 

 It is easily recognized by its transversely striated appearance, and is about equally 

 thick in the umbella and in tlie peduncle, where it abuts against the compartments 

 of these two subdivisions of the body. At alternating points to these it is a solid 

 mass over the entire diameter of the shaft, but is broken in continuity by the 

 muscular cords (fig. 52, r), which are embedded in it. At the posterior end of 

 the peduncle it is perforated (fig. 51, c') and much reduced in quantity by the 

 anastomosing channels (r"), and is considerably thinner than in front at the trans- 

 verse face of the adherent disk, and is, moreover, deeply pitted there by very 

 irregular indentations which give the inner surface the appenirance of a network 

 (fig. 19, T^). 



59. The miiscular cords are the last objects which will occupy our attention 

 here. From their peculiarities and high degree of development and differentia- 

 tion, they present the most urgent claim for** our consideration. They are by far 

 the most eminently specialized muscular organs to be found in the whole class of 

 Acalephse. Their structure will not be entered into here, as it belongs to the 



4 Februa-y, 1877 



