222 



HYDROID^. 



Part IV. 



Fig. 32. 



the proboscis, is several times thicker than the outer one («), hut gradually thins 

 out, till, in the cylindrical part of the pedicel, the two are 

 of equal thickness. Ten, fifteen, twenty, or twenty-five pedi- 

 cels spring from a large, thick, and short peduncle (PI. XXT. 

 Fig. 8", n), which projects directly from the sides of the body. 

 This form of grouping may be compared to a very short 

 raceme, as the term is used in reference to plants. Usually 

 these bunches are attached to the stem, nearly on the same 

 level, and just below the tentacles {Fig. 2, A B D F H), but 

 frequently the crowded groups extend downward, either con- 

 tinuously or in detached masses,^ over one third of the dis- 

 tance toward the base (wood-cut 32). When the stem is 

 contracted, these scattered groups are brought together so 

 as to appear as if they originated nearly upon the same 

 level [Fig. 2, G). After maturing their young within the 

 cavity in which they arise, and casting them forth, the me- 

 dusoids shrivel and die, without ever becoming free, or 

 assuming a form at all resembling common free MedusEe. 



SECTION III 



EMBRYOLOGY OF CLAVA LEPTOSTYLA. 



According to our notes, the time of breeding is June and July, but whether 

 it begins earlier and lasts later remains doubtful. The first individual of a new 

 colony always originates as an egg, in the body of a medusoid (PI. XX. Fig. 11, b^). 

 We have not investigated the mode of development of the egg, and can only say 

 that, just before segmentation, it is situated in the cavity of the disk of the 

 medusoid, and rests there, neither attached to, nor surrounded by, any membrane. 

 Being crowded between the disk and the proboscis, the two or three eggs are 

 more or less mutually flattened, and irregularly polyhedral. The yolk (h^) is a 

 dense, grayish, finely granulated mass, lighted up on one side by a large Purkin- 

 jean vesicle (^*). The latter is equal, in diameter, to about one third of the egg. 



^ A hydra of Clava leptostyla, similar to Fig. 

 2, A, PI. XXI., to show tlie groups of meduste 

 (6 c d) attached along the stem tor some distance 



below the head ; a, a group in the place where 

 they have usually been observed. Drawn from 

 nature by II. J. Clark. 



