380 REPORT—1863. 
mulus. Upon the proximal edge of the leaflet these processes usually remain 
in an imperfectly developed state, though they are occasionally equally well 
developed on both edges. The processes which are thus developed on the 
edges of the leaflet are in all respects similar to the lateral nematophores of 
the trophosome (see above, p. 355). They are filled, like these, with soft 
granular protoplasm, in which is immersed a cluster of fusiform thread- 
cells, and which is in direct communication with the ccenosarc filling the cavity 
of the leaflet. They are also, like these, perforated at their extremity by 
an oblique aperture; but I have never seen the nematophores of the cor- 
bul emit, like those of the trophosome, pseudopodial prolongations of their 
contents. ; 
The leaflets, as they increase in size, direct themselves vertically from the 
upper surface of the ramulus, and those of one side arch over so as to approach 
those of the opposite. They are at first free, but they afterwards become 
intimately united at their edges, the nematophores continuing to project as 
tooth-like processes, and forming an elegant serrated ridge between every two 
leaflets. Ultimately the leaflets of one side coalesce with those of the other 
by their summits, and thus form a completely closed chamber (D). 
As the young leaflet continues to grow, its cavity becomes partially divided 
by a septum (Fe), which stretches across from the outer to the inner side, 
parallel to the axis of the leaflet, but always nearer to the proximal edge. 
At the free end of the leaflet the septum is incomplete ; so that here the 
contents of the cavity at one side of the septum communicate with those 
upon the other side, both sides communicating at the base of the leaflet with 
the common cavity of the ccenosare. 
In the receptacle thus formed the gonangia are produced. They spring 
from the upper side of the metamorphosed ramulus, near the point where 
the leaflet leaves it, and represent the hydrothece which exist on an ordinary 
ramulus, and whose place they here take. They begin to be produced at an 
early stage of the corbula, and may be easily examined in the young corbula 
before it has become closed (B 6, C4). The metamorphosed ramulus gene- 
rally remains unchanged for a short distance from its origin, and may be 
here seen bearing one or two ordinary hydrothece. 
About twelve gonangia are usually contained in each corbula. They are 
of a very simple type (G), of a regular oviform figure, and with their chitinous 
walls thin and delicate. Each gonangium seems to contain but a single 
sporosac, which soon comes to occupy almost the whole cavity of the 
gonangium. A long, nearly cylindrical spadix extends almost from the base 
to the summit of the sporosac, passing in the male through the axis of the 
mass of spermatogenous tissue, but in the female pushed to one side by the 
development of the large single ovum, which here occupies almost the whole 
remaining portion of the cavity of the sporosac. 
There may appear some difficulty in deciding as to whether the corbula 
ought to be regarded as properly belonging to the trophosome or to the 
gonosome. The truth is, that it holds a place exactly intermediate between 
the two, and may in this respect be compared to the bracts in plants; for 
these are in the same way intermediate between the ordinary leaves and the 
proper floral verticils. As the bracts, however, are usually treated of in 
connexion with the ¢nflorescence, whose limitation they frequently determine, 
' we shall perhaps here also find it convenient to speak of the corbula in con- 
nexion with the gonosome rather than with the trophosome*, 
* In a very ingenious paper, ‘On the Morphology of the Reproductive System in the 
Sertularian Zoophytes,” by Prof. E. Forbes (Ann. of Nat. Hist. 1844, vol. xiv. p. 385), 
