250 DKOSEEA ROTUNDIFOLIA. Chap. X. 



proves that the spiral vessels of the central trunk may- 

 be divided, and yet the motor impulse be transmitted 

 from the distal to the basal end ; and this led me at 

 first to suppose that the motor force was sent through 

 the closely surrounding fibrous tissue ; and that if one 

 half of this tissue was left undivided, it sufficed for 

 complete transmission. But opposed to this conclusion 

 is the fact that no vessels pass directly from one side 

 of the leaf to the other, and yet, as we have seen, if 

 a rather large bit of meat is placed on one side, the 

 motor impulse is sent, though slowly and imperfectly, 

 in a transverse direction across the whole breadth of 

 the leaf. JSTor can this latter fact be accounted for 

 by supposing that the transmission is effected through 

 the two inosculations, or through the circumferential 

 zigzag line of union, for had this been the case, the 

 exterior tentacles on the opposite side of the disc 

 would have been affected before the more central ones, 

 which never occurred. We have also seen that the 

 extreme marginal tentacles appear to have no power 

 to transmit an impulse to the adjoining tentacles ; yet 

 the little bundle of vessels which enters each marginal 

 tentacle sends off a minute branch to those on both 

 sides, and this I have not observed in any other ten- 

 tacles; so that the marginal ones are more closely 

 connected together by spiral vessels than are the 

 others, and yet have much less power of communi- 

 cating a motor impulse to one another. 



But besides these several facts and arguments we 

 have conclusive evidence that the motor impulse is 

 not sent, at least exclusively, through the spiral 

 vessels, or through the tissue immediately surrounding 

 them. We know that if a bit of meat is placed on a 

 gland (the immediately adjoining ones having been 

 removed) on any part of the disc, all the short sur- 



