42 



THE POLYPI. 



§^ 31, 32. 



With Eschar a there are, moreover, two fasciculi in each cell, which movö 

 its operculum, and thus close the entrance of this cavity Z*'' 



§31. 



Locomotion is performed bv the Polyps in various ways. 



With the Hydrae, by their long-stretching arms ; with Actiniae, by the 

 contractions of the disc of their foot ; ^" while the Edwardsiae, having elon- 

 gated bodies which are not attached by a foot, progress by vermiform 

 movements.*-' With Cristatella mirabilis, the whole colony moves itself 

 along by the foot-like basis, like the Actiniae.^'^ 



Some Polyps, at a certain period of their development, move freely in 

 the water by discoid contractions of their body, like the pulmograde 

 Acalephae.'^' 



§ 32. 



A very remarkable peculiarity is the presence, in certain Bryozoa, of 

 organs shaped like a bird's head, and which swing to and fro at the base 

 of their cells. In some species, these organs have the form of lobster's 

 claws, being composed of both a fixed and a movable piece. This last is 

 corneous, and moved by a muscle which arises from a cavity in the first. 

 It is not yet known by what means either this beak is opened, or the 

 whole organ moves to and fro.*^' 



Equally unknown is the function of these singular organs, the move- 

 ments of which persist after the death of the animal, and of which, there- 

 fore, they are independent. *^> They are perhaps organs of defence or pre- 

 hension, and analogous to the Pedicellarice of the Echinoderms. 



muscles of Plumatella (Comp. rend. XII. 1841, p. 

 724 ; Mailer's Arch. 1842, p. cc.\).* 



B Milne Edwards, Anu. d. So. Nat. loc. cit. p. 

 24, pi. I. fig. 1, e. 



1 Berthold, loc. cit. p. 14. 



2 qaatrefages, Ann. d. Sc. Nat. XVIII. p. T4; 

 also Forbes, Ann. of Nat. Hist. VIII. 1842, p. 243. 



Ü I have been able to confirm the observation of 

 Dalyell (Froriep's Notizen 1834, No. 920, p. 276) 

 upon this motion in Cristatella. Trembley, also, 

 has observed that the corallura of Plumatella 

 cristata moved half an inch in eight days (see 

 liis jM^moire pour servir a I'Hist. des Polypes d'eau 

 douce, 1775, p. 298). 



4 See the observations of Steenstrup (Ueber d. 

 Generationswechsel, 1842, p. 20) upon Coryne fri- 

 titlaria ; also those of Van Heneden (Mem. sur 143 

 Campaiiulaires, 1843, \i. 29, or Froriep's neue Noti- 

 zen, 1844, No. 663, p. 38) upoa Campanularia ge- 

 latinusa. 



* [ § 30, note 5.] Allman (Report Brit. Assoc. 

 1850, p. 314) has described a very complete mus- 

 cular system in the fresh-water Bryozoa. In the 

 species with bilateral lophophores, there are seven 

 distinct sets : 1. Retractor muscles of the polypide; 

 2. The rotatory muscles of the crown ; 3. The 

 tentacular muscles ; 4. The elevator muscle of the 

 valve ; 5. Superior parieto-vaginal muscles ; 6. 

 Inferior parieto-vaginal muscles ; 7. Vaginal sphinc- 

 ter. The walls of the stomach also contain circular 

 muscular fibres. 



1 These organs were first described by Ellis 

 (Essai sur I'Hist. Nat. des Corall. 1756, p. 51, pi. 

 XX. fig. A). Nordmann (Observ. sur la Faune 

 Pontique, 1840, p. 679, pi. III. fig. 4) has described 

 and figured them with much accuracy. In Cel- 

 laria avicularis, Bicellaria ciliata and Flustra 

 avicularis, they are formed like lobster's claws. 

 In Retepora cellulosa they are pincer-like, and in 

 Telegraphina they are articulated stings. See 

 also Krohn in Froriep's Notizen, 1844, No. 533, 

 p. 70. 



For the organs having the form of a bird's head 

 and a lash, and which are present in certain Bry- 

 ozoa, see also Van Beneden, Recherch. sur I'anat. 

 &c., des Bryozoaires, in the Nouv. M^m. de Brux- 

 elles, XVIII. 1845, p. 14, pi II. III., and Reid in 

 the Ann. of Nat. Hist. XVI. 1845, p. 885, pi. XII. 



2 Darwin''« Voyage of the Beagle, 1844, pt. I. 

 p. 252.t 



With Paludicella, the muscular system is some- 

 what different ; there are here five sets, — the 1st. 

 5th, 6th, and 7th of the preceding, and the parie- 

 tal muscles. But with the 1st there is here only a 

 single instead of a double fasciculus. — Ed. 



t [ § 32, note 2.] See Ilincks (Ann. Nat. Hist. 

 Vm. 1851, p. 353), who regards these avicularia 

 as organs of defence, and has observed them seiz- 

 ing and retaining foreign bodies. — Ed. " 



