134 



MELICERTUM CAMPANULA. 



(Fig. 209), and taper raj)icl]y ; they are thickly covered with lasso- 

 cells. 



Artificial fecundation of these Medusas can be very readily made by 

 keeping males and females for a day or two together in a glass jar, 

 Avhen we shall find, swimming near the bottom, innumerable spherical 

 embryos (Fig. 210), in which the spheres of segmentation are still 



visible ; these elongate (Fig. 211), a cavity is formed at the blunt end, 

 and we have a somewhat pear-shaped embryo, strongly ciliated, with 

 walls of uniform thickness (Fig. 212), swimming about with great ve- 

 locity ; these embryos attach themselves by the blunt end (Fig. 213), 

 and soon elongate, as in the two middle figures of Fig. 213 ; the slen- 

 i-ig. 214. der extremity next swells (Fig. 214), and this is the 



first trace of the sterile Hydra head. The waU of 

 this swelling soon becomes somewhat indented, as 

 in Fig. 214, where we have some of the successive 

 stages of the sterile Hydra, until it forms a small 

 horny bell, covering only the base of the long, ster- 

 ile Hydra head, which terminates with ten stout, 

 short tentacles, connected by a web. This Hydra- 

 rium differs considerably from that of Lafoea, but it 

 still has sufficient resemblance to show their con- 

 nection ; it is one of the easiest to raise, the 

 Planulae are very hardy, and the development of 

 the Hydrarium is readily followed. It grows in 

 small tufts, which after six months had not attained a greater height 

 than one third of an inch. 



Greenland (Fabricius) ; Massachusetts Bay (Agassiz). 

 Cat. No. 351, Grand Manan, L. Agassiz. Medusa. 

 Cat. No. 373, Nahant, 1863, A. Agassiz. Medusa. 

 Cat. No. 448, Nahant, 1864, A. Agassiz. Medusa. 



Fig. 210. 

 Fig. 211. 

 Fig. 212. 

 Fig. 213. 

 Fig. 214. 

 developed. 



Spherical emWyo. 



The same, somewhat more advanced. 



The same, immediately before becoming attached. 



Group of embryos attached, in different stages of development. 



Diiferent stages of growth, beyond those of Fig. 213, till the sterile Hydra is fully 



