RADIATA. | 33 
Finally, the union between the segments is more and more reduced, until 
they separate like a pile of hemispherical cups, as in Diagram, jig. 6, when 
they are seen to be separate animals in an inverted position; in fact, the 
young or larve of Aurelia (pl. 76, fig. 74). These larvae (constituting the 
supposed genus Zphyra) are about a line in width, and continue growing 
and passing through such a change as to give it the structure of the adult, 
which it acquires when about an inch in size. It is not precisely known 
what becomes of the polypiform head of the Strobila (Diagram, jig. 5), but. 
the base is said to produce a new set. 
It appears from these facts that the animal (Diagram, jig. 1) hatched 
from the egg of a medusa, does not become a free medusa, but a kind of 
polyp, Scaphistoma strobila, which does not produce its like, but from 
which meduse are developed. The polypoid nwrse, as it has been termed, 
is uniformly an undeveloped female, whilst of the resulting medusx, some 
are male and some female. The nurse, like the adult medusa, has the 
power of increase by budding. 
(" The annexed jig. 1 represents an 
individual of the presumptive genus 
_ Coryne, placed in the family Tubu- 
laride (p. 27). The head is a six- 
oN armed hydroid, beneath which are 
four quadrate, bell-shaped bodies, 
which are not organs, but distinct 
1 2 8 
individuals of an entirely different 
form from the hydroid. In the concavity of each is suspended a quadrate 
stomach, as shown in jig. 2. These bodies have an independent motion, 
sucking the water in, and throwing it out like the Meduse. They finally 
detach themselves, and swim freely like medusze, to which they bear a close 
resemblance. Steenstrup, who observed this species in Iceland, found 
larger individuals (jig. 3), which he considers the adult medusaform of the 
former, in which one of the angles bears a lobed organ and two threads, © 
which he regards as female generative organs. Steenstrup regards Coryne 
as “a previous generation of preparative nurses, which are so far asexual, 
inasmuch as that their generative organs are not developed.” 
Forbes describes two minute British species allied to jig. 3, under the 
generic name of Steenstrupia, suggesting that they may be a stage in the 
history of some hydroid form. 
Class 2. Zoophyta. 
The Zoophyta are chiefly marine; some species are sedentary and others 
free, some live as single independent animals, and others are collected 
together in large colonies, the base of the stems being united. Some are 
without a hard support, others secrete a stony skeleton, which is named 
coral (CORALLUM, CORALLA in the plural). 
The corallum is not usually external like the shell in the Mollusca, as is 
popularly supposed, but an internal secretion “ entirely concealed,” in the 
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