64 
The gonophores may present a further remarkable condition, iit 
having a number of them grouped together and included in a 
common receptacle formed by modified ramuli, as in Plumularia 
cristata . 
Besides the above types, certain interesting modifications of form 
are presented by the sporosacs. 
In these the manubrium may be 
1. a simple diverticulum from the coenosarc or the blastostvle, 
as in Hydractinia, Laomedea, &c. 
2. It may be irregularly lobed, as in Plumularia pinnata . 
3. It may send off from its base true gastrovascular canals, as in 
Cordylophora. 
4. It may be completely suppressed, while well-developed gastro- 
vascular canals spring from the base of the sporosac. This condi- 
tion we find in Campanularia caliculata. 
In the development of the embryo, we are probably justified in 
distinguishing two distinct types, though further observations will 
be needed before we can consider the generalization involved in 
this assertion as absolutely established. 
1. The embryo may be developed directly from the whole vitellus, 
and will then always(?) present the form of a ciliated conical body. 
2. The embryo may be developed directly from only a part of the 
vitellus, and will then always (?) present the form of a non-ciliated 
actiniform body. 
2. On the Focal Adaptation of the Eye in Man and some 
Animals. By Dr James Black, F.G.S. Illustrated by en- 
larged diagrams. 
After several introductory observations on the refractive condition 
of the human eye in infancy, in the prime of life, and in old age ; 
and also in some tribes of artizans, in shepherds, and in mariners, 
with notices of the focal adjustment in the eyes of oxen, common 
fowls, and in fishes, as the cod and haddock, the author examined the 
different theories which have been advanced to account for this adapt- 
ing power, and expressed his strong opinion that the external mus- 
cular apparatus was the principal and initiating agent. 
