148 LECTURE VUI. 



upon its middle part : this is most apparent, being thickened when 

 the filament contracts, at which time the Avhole filament is obviously 

 thicker. When the action ceases and the filament is relaxed, the 

 distance between its fixed points being diminished, as happens to the 

 longitudinal fibres when the polype is retracted into its cell, such 

 fibre fails into undulations. The thickening of the muscular fibre in 

 the act of contraction, and its folded state when it I'elaxes, before the 

 antagonising muscles have restored the extremities of the contracted 

 fibre to their ordinary distance, has been observed in other low 

 organised animals, as small Filarite.* The higher organised subjects 

 selected by MM. Prevost and Dumas, were less favourable for this 

 delicate experiment, and they consequently mistook the zig-zag re- 

 laxation of the muscular fibre for its act of contraction. In Notamia 

 and Anguinaria a faint striation has been observed on the ultimate 

 fibre. Minute appendages called "pedicellariae" are fixed to the cells 

 in most Bryozoa. Ellis, who has figured them in the Cellularia avi- 

 cularis, compares them to " a bird's head with a crooked beak, opening 

 very wide:"f they consist of a fixed and a moveable nipper, like a 

 crab's claw, the latter being worked by muscles arising from the in- 

 terior of the fixed portion. In the Retepora celhdosa the pedicellarias 

 resemble a pair of pincers : in the Telegraphina they are simple one- 

 jointed spines. The entire pedicellariae, in many Bryozoa, have oscil- 

 latory movements, more or less rapid and regular, in ditFerent species. 

 The removal of the polype from the cell to which they may be attached 

 does not affect these movements : and if a chelate pedicellaria be cut 

 off, its moveable nipper continues for some time to open and close.| 



Dumortier describes two nervous ganglions near the mouth of the 

 Plumatella cristata, and Nordmann similar ganglions in Plum, 

 campanulata and Tendra zostericola. V. Beneden believes that he 

 has traced an oesophageal nervous collar in the Alcyonella § ; but 

 Dr. Farre was unable to satisfy himself as to any definite trace of a 

 nervous system in the marine Bryozoa, which he has so ably ana- 

 tomised. The reaction of stimuli upon the contractile fibre was, 

 however, a striking phenomenon in these. The animal retires into 

 its cell on the slightest alarm, and refuses to expose itself to watei* 

 which has become in the least degree deteriorated. Dr. Farre has 

 observed the creeping of a very small animalcule over the top of one 

 of the closed cells to be followed instantly by the shrinking of the 

 soft parts beneath. But the nervous system is indicated in these 

 little polypes by something more than reflex phenomena : they seem 



* CXXVUI. p. 261. t XCVn. p. 3G. pi. XX. A. 



X CXXIX. p. 201. § Cited in XXIV. p. 34. 



