Dr. Rcid on the Development of the Mcclusre. 31 



about to be described, indicative of their splitting transversely into 

 young Medusae. In the beginning of February of the present year, 

 the upper part of the body of some of the larvae of the first colony 

 became cylindrical, considerably elongated and much diminished 

 in diameter, with thickly-set rings forming at the top. From the 

 circumference of the rings first formed eight equidistant lobes or 

 rays began to grow, the rings increased in size and became of a 

 reddish brown colour, the tentacula gradually wasted away, and 

 in the course of eight days the young Medusae were beginning 

 to detach themselves in the manner described by Sars. While this 

 was going on at the upper part of the body, the process of elon- 

 gation and the formation of new rings was proceeding downwards, 

 as represented in PL VI. fig. 14, so that thirty or forty rings, 

 each of which was about to become a young Medusa, could be 

 counted on the body of one larva at the same time, and the body 

 in some cases measured three-fourths of an inch in length. At 

 this period the upper part of the body was of the form of an in- 

 verted pyramid, and had a distinctly reddish brown colour. As 

 the grooves separating the rings increased in depth, it was ob- 

 served that the body of the young Medusa above was at last 

 attached only to the upper margin of the lips of the one below. 

 Fig. 15 is a greatly enlarged representation of one of these young 

 Medusae immediately after it had separated itself from the body 

 of a larva. A small proportion, probably not above one-sixth or 

 one-seventh of the larvae, underwent this process of splitting into 

 young Medusae, and in no case that I observed did it extend 

 through the whole length of the body of the larva ; for a portion, 

 often very small, at its attached end did not become ringed 

 (fig. 14 a), threw out new tentacula before the young Medusae 

 last formed were detached, and it continued to live as a 

 larva. Some of the larvae of the other two colonies obtained in 

 July of the preceding year began to yield young Medusae about 

 the middle of March, and exactly in the same manner as in the 

 first colony. A fortnight, or more, generally elapsed, after the 

 commencement of the separation of the young Medusae in a 

 larva, before the process was finished. 



The general appearance and habits of the young Medusae im- 

 mediately after they have detached themselves from the larvae 

 have been described already by Sars, but there are various parts 

 of its structure which stand in need of additional elucidation. 

 External to the quadrangular mouth occupying the centre of the 

 lower surface of the body of the young Medusa (fig. 15) are four 

 bifid hollow processes, placed at equal distances from each other, 

 and adhering by the end of their undivided portion to the inner 

 surface of the inferior wall of the stomach (fig. 15 a). The in- 

 ferior wall of the stomach, which forms also the inferior surface 



