406 Dr. F. Miiller on a Hybrid Balanus. 
culum when the hand, for example, is passed between them 
and the window. 
It is remarkable that individual animals are much shyer, 
and others, again, bolder than the rest—that the former always 
remain longer closed, and the latter venture out more quickly, 
and even become accustomed to the passage of the hand at 
regular intervals. I may remark, in passing, that I detected 
similar mental differences between the animals of a group of 
EHupomatus floribundus. 
Diba when, in repeating these observations, I was watching 
the action of the cirri in some examples of Balanus armatus 
which I had taken freshly from Cartjoa and cleaned from their 
coating of sponge, I saw that one of them suddenly ceased strik- 
ing with its cirri, held them for some seconds immoveable 
and widely spread out, and during this period the penis ex- 
tended to its utmost length and moved about as if feeling or 
seeking for something. I then no more disturbed my animals 
with the shadow of my hand, in order, if possible, to see this 
spectacle repeated; and in fact I soon witnessed the same el 
nomenon again, not only in the same animal, but also in three 
or four others. I now placed these ardent animals close to- 
gether, in order to facilitate their reciprocal copulation ; but as 
often as the elongated penis came within reach of the cirri of 
a neighbour, it was pushed to and fro by them, and the animal 
did not remain quiet so as to give access to it. Upon this I 
examined two of the animals, and found the entire canal of 
the penis densely filled with semen; but in both there were 
also ova which had already completed their segmentation, and 
consequently no longer required fecundation. With the penis — 
so filled, when extended to its utmost length, semen must 
certainly have been expelled from it (which I could not have 
seen upon a white saucer); but at the same time, from the 
length of the penis, usually extended in a lateral direction, 
this semen would be removed from the vortex produced by the 
cirri of the same animal and placed within reach of neigh- 
bouring animals which might require it. It is remarkable 
that, although at that time I made the observation upon four 
or five animals simultaneously, I have been unable to repeat 
it, notwithstanding that I have repeatedly looked for it in nu- 
merous fresh animals. 
The second observation which seems to prove that fecunda- 
tion sometimes occurs even between different species of Ba- 
lanus is as follows :—Among the Balan? obtained on Carijoa, 
which I had at the first glance determined as B. amprovisus, 
var. assimilis, there was one that struck me by a somewhat 
reddish coloration, such as I had never seen in this infinitely 
