C.iAP. IV. THE PENNARIDvE. 281 



The mode of growth of the main stem and branches is simply this; the main 

 stem, carrying its great terminal individual {Fig. 1, d) continually onward from the 

 beginning, gives off, alternately right and left, a branch, which, at first, bears only 

 a single hydra of the largest kind {Fig. 2, B). The main stem continues to give 

 off branches in this manner, while each branch, carrying outward its great terminal 

 hydra, gives off", always on its up^oer side, and in one line, a succession of pedun- 

 culated individuals (G F E D C), in such a manner that the youngest is always 

 next to the end of the branch. In consequence of this mode of growth, the 

 lowest branches are the longest, and bear the greatest number of individuals, Avhile 

 those above are successively shorter; but it is very seldom, and owing to accidents, 

 as examination of the branches shows, that a perfect specimen, illustrating the 

 whole succession of individuals as they originally budded forth, can be found. We 

 have counted as many as twelve individuals on one branch ; but, inasmuch as the 

 branch was broken off" at the top, and, moreover, sprang from the main stem at 

 the sixteenth interval from the base, we may safely infer that the lowest branch 

 bore twenty or twenty-five individuals. The branches themselves give off" secondary 

 branches, as the third branch from the base in Fig. 1 shows; but how extensively 

 this occurs, we have not ascertained. Since, however, the cases observed were 

 isolated, the lower branches of the main stem rem.aining simjile, we suspect that 

 this sort of secondary ramification is only an occasional phenomenon. 



The medusa. — The oldest medusa which we have observed had an oval oblong 

 figure {Fig. 2, G, d^), and measured about one twelfth of an inch in length. It 

 had a large proboscis (/), similar in shape to itself and was nearly half as long. 

 At four equidistant places, a radiating chymiferous tube {h) diverged from the base 

 of the proboscis, and terminated in a circular tube (e^) at the edge of the disk. 

 What seemed to distinguish this medusa from all other Medusa, among the Tubu- 

 larians, was the position of the ovaries {e c^), which, instead of being on the 

 proboscis, were near the peripheric, or outer end^ of the chymiferous tubes ; these 

 oi'gans were, however, not so far developed as to show their sexual character, and 

 may be only specialized cells, as in Zanclea. They occupied about one third of 

 the length of the tube, and had an elongate oval, or fusiform shape. There were 

 also four globular, papillate tentacles (^17), like those of Zanclea, one of which stood 

 opposite the end of each radiating tube. The disk was perfectly transparent, and 

 free fi-om the red, granular, longitudinal lines, which ornament the surfoce of some 

 of the Tubularioid medusas. 



In another chapter it will be shown, that the Hydroids described by Ayres 

 and Leidy, under the names of Globicops and Eucoryne, and by McCrady, lender 

 the name of Pennaria, are very closely allied, but not generically identical with 

 Pennaria, though belonging to the same family. 



VOL. IV. 36 



