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the four radiating canals described by Loven, nor any other repre- 
sentative of the gastrovascular system of a medusa. When the con- 
tents have attained a sufficient degree of maturity they escape, as 
has been already shown by Loven, through an aperture which 
makes its appearance in the centre of the tentacular crown. 
If we follow the development of these extra-capsular sporosacs, 
we shall find, as Loven has already pointed out, that they are ori- 
ginally produced within the capsule. They are here indistinguish- 
able from the ordinary intra-capsular sporosacs, and originate, 
exactly like the latter, as buds from the blastostyle. The blastostyle, 
however, instead of remaining stationary, as in the ordinary gono- 
phores, grows upwards through the aperture of the capsule, carrying 
out with it the most mature sporosacs, or those which are formed 
nearest its summit, and which thus become extra-capsular, de- 
veloping from their ectotheque, while in this situation, their little 
tentacular crown, and, after the discharge of their contents, withering 
away, to be replaced by others. 
Notwithstanding the resemblance which the extra-capsular sporo- 
sacs, with their investing ectotheque, bear to a medusa, they will far 
more easily admit of a comparison with the ordinary intra-capsular 
sporosacs. Of the two membranes composing their walls, the inter- 
nal is undoubtedly the endotheque, while the external is just as 
obviously an ectotheque, differing, however, from that of an ordinary 
sporosac, in its being provided, for the liberation of its contents, 
with a definite orifice surrounded by rudimental tentacles. 
We have not here, more than in the intra-capsular sporosacs, 
any representative of an umbrella ; and I confess myself quite unable 
to understand the radiating canals figured and described by Loven. 
If this excellent zoologist has not been deceived as to the existence 
of such canals, they will probably be identical with the coecal proces- 
ses from the spadix which I have already described as occurring in 
the sporosacs of several species of hydroid zoophytes. 
Sertularia tamarisca , Linn. 
Sertularia tamarisca , like most of the hydroid zoophytes, is 
strictly dioecious, but it further presents the remarkable character 
of having its male and female gonophores totally different from one 
another in form, an important fact as regards the zoograph ical 
characterization of the species. 
