94 BALANIDJ3. 



transparent membrane, to which the above slight circular 

 expansion is attached, acts as such. This description very 

 closely agrees with that given of these organs in Bed. rugosus 

 of Gould, (B. crenatus ?) by Dr. Leicly,* who first disco- 

 vered the eye in the adult cirripede, but he did not 

 observe the ophthalmic ganglion. These eyes differ from 

 those in some of the genera of the Lepadidse, only in the 

 greater length of the optic nerve, and by standing laterally 

 further apart from each other. 



I may here mention that I tried a few simple experi- 

 ments on the senses of Balanus balanoides, B. crenatus, 

 and Chthamalus stellatus. I found these three species very 

 sensitive to shadows, that is, to an object like my hand 

 passing even quickly, and at the distance of about a foot, 

 between them and the source of the light. t They were in- 

 different to a gradual change from bright to obscure 

 light ; but instantly perceived and drew in their cirri, when 

 my hand was passed between the basin in which they were 

 kept and the window, even when this was tried rather late 

 on a dusky evening ; and likewise when my hand was passed 

 between them and a single candle. I took, of course, the 

 precaution of passing my hand in other directions, but this 

 never produced any effect. These species are moderately 

 sensible to any vibration in the vessel in which they were 

 kept, but they were indifferent to noises made in the 

 air, or in the water. I found it impossible to touch, under 

 water, an individual shell ever so lightly with a needle, 

 without all the immediately surrounding individuals, when 

 several adhered together, perceiving it, and retracting their 

 cirri : it made no difference whether the one touched had 

 already withdrawn its cirri and was motionless : from this 

 fact, and from seeing that a similar but slighter effect 

 was produced by touching the rock on which the specimens 

 adhered, I infer that the perception by the others of 

 the one being touched, is communicated by vibration. 



* 'Proceedings of the Acad. Nat. Sciences of Philadelphia/ vol. iv, 1848, p. 1. 

 I may add that I have, also, observed the supra-cesophageal and ophthalmic 

 ganglions in Bed. prrforatus. 



f I find that this fact was long ago observed by Von Siebold, ' Anatomie 

 Comparee,' torn, i, p. 434. 



