422 REPORT—1863. 
this plate to become perforated in the centre, while its contractions rendered 
it easily recognizable as a velum. Next, four tentacles began to sprout out 
from the circumference of the velum, and then four others between them, 
while a gastrovascular system, consisting of radiating and circular canals, had 
become visible, and the shallow manubrium might be seen in the bottom of 
the cavity. The first four tentacles were only temporary, being destined to 
disappear during the growth of the young medusa, while the second set 
remained as short rigid filaments. In the next place four other tentacles, 
long and eminently contractile, made their appearance, as permanent organs, 
near the bases of the temporary ones, while lithocysts had become developed 
near the bases of both the rigid and the contractile permanent tentacles, 
Finally, the manubrium elongated itself in the cavity of the umbrella, where 
it was itself borne on the extremity of a peduncle-like process from the roof ; 
and the form of the adult Lyriope Catharinensis—the most abundant medusa 
of the surrounding seas—was thus ultimately attained. 
Here, again, as indeed Miiller himself admits, there is no evidence in 
favour of this being a case of direct development from the egg, the earliest 
stage observed having been found free in the sea, and certainly with none of 
the characteristics of an ovum; so that it is at least as likely that it should 
have been a free bud as a developing ovum. 
Thus far then not a single recorded observation affords evidence that the 
gymnophthalmic meduse ever originate directly by the development of an 
ovum. We have, however, one observation, and only one, in which the 
development of one of these medusze has been traced backwards uninter- 
ruptedly to the egg and the parent medusa, without the intervention of any 
intermediate polypoid form. 
For this important observation we are indebted to Claparéde*, who obtained 
on the west coast of Scotland a species of Lizzia whose manubrium was 
loaded with eggs, some in an early stage, with the germinal vesicle and. 
germinal spot still visible, while others contained an embryo in various stages 
of development. Similar ova, with the contained embryo, he also found 
floating free in the sea. 
The embryo, while still confined within the vitellary membrane, presented 
all the features of a young medusa: from the centre of the bell-shaped um- 
brella there depended a thick-walled manubrium, whose cavity extended itself 
into four radiating gastrovascular canals, which ran in the substance of 
the umbrella, and opened at the margin into a circular canal, while round the 
margin were to be seen the rudiments of eight tentacula. Claparéde’s ob- 
servations on the development of the embryo did not extend beyond this 
point; it is clear, however, that but slight changes were now needed to 
convert it into the form of the parent Lizzia. 
VI. Hereromerism oF THE INDIVIDUAL. 
From the facts now mentioned, it will be at once apparent that the Hy- 
droida present to a most remarkable extent a phenomenon which may be 
described as the heteromerism of the individual. The term individual, in its 
proper zoological conception, must be understood in the sense so happily 
insisted on by Huxley, when he defined it as “ the total result of the deve- 
lopment of a single ovum” +. It is the true logical element of which the 
* Zeit. f. wissen. Zool. 1860, p. 401. 
+ Huxley, “Report on the Researches of Professor Miller into the Anatomy and Deve- 
lopment of the Echinoderms,” Ann. and Mag. of Nat. Hist. July 1851; and “ On Animal 
Individuality,” 7d. June 1852, 
