452 Dr. W. B. Carpenter on the Structure [Apr. 6, 



arms of Actinometra armata and A. nigra — two pairs of branches running 

 on each side towards the dorsal surface, and two towards the ventral, 

 where he has distinctly traced their ramifications as far as the leaflets 

 bounding the ventral furrow. Prof. Greef , on the other hand, describes 

 the whole epithelial floor of the ventral furrow as a nerve, on the ground 

 that its histological character resembles that of the nerves of other 

 Echinoderms. 



Having recently had an opportunity of examining at Wiirzburg the 

 very thin sections prepared by my son, I can say with certainty that the 

 fibrillar band is quite distinct from the layer of columnar epithelium which 

 it underlies ; but it appeared to me to send off very minute fibrils that 

 pass up between the cells of which that layer is composed. 



To myself it appears by no means improbable, looking alike to its 

 position and to its histological characters, that this band is a nerve ; but 

 having regard to its immediate proximity to the sensory (ventral) surface, 

 and to its separation from the muscles by the interposition of the triple 

 canal-system, I cannot but think it more likely that it is functionally 

 related rather to the former than to the latter — in other words, that it 

 is an afferent rather than a motor nerve. 



As it seemed to me that important evidence might be obtained on this 

 point from experiments made on the living animal, I took the opportunity 

 afforded by my recent visit to the Zoological Station at Naples to insti- 

 tute such experiments ; the results of which I am desirous of appending 

 to my Paper, as they seem to me to place the doctrine advocated in it 

 beyond reasonable doubt. 



Every one who has had the opportunity of observing the habits of the 

 living Antedon well knows the peculiarly rhythmical and symmetrical 

 swimming action which it executes when it spontaneously leaves or is 

 detached from the anchorage afforded by the grasp of its dorsal cirrhi. 

 Each of its five rays divaricates into two arms, which may be characterized 

 (like the two legs proceediug from the human trunk) as the right and the 

 left respectively ; and the act of swimming consists in the alternate 

 consentaneous advancement of the Jive right and then of the Jive left 

 arms, each of which is bent forwards in a curve which resembles that of 

 the swan's neck in its graceful arch, and is then straightened backwards. 

 The perfect similarity of the movements of all the five arms that work 

 together, involving the conjoint contraction of several hundred pairs of 

 muscles, seems to me to point almost certainly to coordination through a 

 nervous centre ; and it will be seen that experiment has fully confirmed 

 that conclusion. 



It will be recollected that the centre of what I regard as the motor 

 nervous system is the quinquelccular organ contained in the centro- 

 dorsal basin, which Midler (who did not recognize its cavitary sub- 

 division) characterized as a heart. Midler's view of its nature is still 



