Chap. VII. • CLYTIA POTERIUM. 301 



still growing, the four channels terminate in the single chymiferous cavity (d). 

 The medusa (i) is so crowded in the calycle, that it is hardly possible to see 

 its connection with the axis unless the whole horny sheath is removed {Fig. 13"), 

 and then we find that only one of the axial canals (c) is in direct communication 

 with the radiating tubes (/), the single channel (c^) of the peduncle being the 

 medium between the two. The whole cavity of the disk is filled by the repro- 

 ductive material, either eggs or spermatic particles. 



From this period onward, the medusa, already recognizable as such, grows com- 

 paratively very rapidly, and, in size, soon surpasses the whole axial portion of the 

 hydra {Fiff. 14). The radiating tubes (/) become more distinct, and the outer 

 wall increases considerably in thickness. Up to the period when the medusa has 

 reached two thirds of its growth, the radiating tubes are simple channels {Fie/. 14, /), 

 but soon after this we find them sending forth, from each side, a row of blind 

 sacs {Fiff. 19, /), so that each canal {e e^ e^) has a pennate appearance. In the 

 males {Fi(/. 19) these diverticles (/) are most frequently opposite each other on 

 any one channel, but in the females {Fiff. 15) they are disposed more or less 

 alternately (/) so as to correspond to the intervals among the eggs (/) ; and 

 they project not only laterally but obliquely toward the interior, as if to form 

 supports for the reproductive mass. Frequently the different channels of the com- 

 pound axis of the reproductive hydra branch above the point of common divergence, 

 as in Fiff. 15, where a short branch (c^) diverges from one of the main channels 

 (c^), near its termination. There is considerable difference among these hydra} in 

 regard to the age at which the diverticles of the radiating tubes of the medusae 

 begin to form; sometimes, in a comparatively young hydra (PI. XXVIII. Fiff. 19, 

 and PI. XXIX. Fiff. 2), the diverticles (/) of the medusJB are quite long, while, in 

 a much older hydra (PI. XXIX. Fiff. 4,/), the diverticles are not more than half 

 as long; or in another {Fiff. 3), nearly as old as the last, they are not developed 

 at all, and the radiating tubes {e) are as yet simple channels. The length of 

 some of these diverticles is remarkable, projecting, as they do (PI. XXIX. Fiff. 2, /), 

 nearly half way across the reproductive mass, and also occasionally branching. In 

 the more highly-developed male medusEe the reproductive mass is internally 

 divided lengthwise, by a furrow (PI. XXIX. Fiff. 2, y), into as many lobes as there 

 are radiating canals, and each lobe is penetrated by the diverticles from a single 

 radiating tube. Whether the reproductive mass is covered by an internal wall, 

 which corresponds to the innermost, or lining wall of the disk of the Hydroid- 

 medusa3, we are not able to say, but incline to believe there is none, inasmuch 

 as the calycles were subjected to prolonged and careful investigation. The wood- 

 cut on the next page, representing an ideal section of Fiff. 2, PI. XXIX., with 

 corresponding letters, will assist in the understanding of the relation of the 



