826 THE ANIMAL KINGDOM. 



a motile phase, it leaves a vesicle containing all its pigment attached to its 

 lorical plate. There is no mouth. The sole organs for catching the living 

 prey upon which an Acinetarian feeds are the tentacles. Of these there 

 are two kinds. One is long, and either pointed or terminated in some 

 cases by a knob ; it may be absent, present with the other kind, or, as in 

 the Actinaria, the sole kind present. It is sometimes motile, and its 

 function is to retain the prey, which it does by bending round it, and then 

 by contraction to bring it within the reach of the suctorial tentacles. It 

 may be denominated therefore ' retinaculum ' (Fangfaden). In Ephelota 

 Trold, one of the Acinetaria which possess only retinacula, it has been 

 observed to shorten, and finally to draw the prey completely within the 

 body. The second kind of tentacle is shorter than the first, and ter- 

 minates either in a trumpet-shaped sucker or in a knob, the latter being 

 probably an extrusion of the axial substance (Maupas). It is said to 

 consist in some cases of a cortical more contractile substance, and a more 

 fluid axis ; in others there is an axial tube. It sucks out the protoplasm 

 of the prey by alternate movements of contraction and elongation, and the 

 granular stream may be traced continuing the line of the tentacle into the 

 body of the Acinetarian for some distance before it is diverted from its 

 course and mingles with the protoplasmic currents of the body 1 . Both 

 kinds of tentacles are eminently contractile, and Podofhrya libera, which 

 has only suctorial, has been observed using them for the purpose of 

 creeping about. As they shorten a spiral fold or line twining round 

 them becomes more and more conspicuous ; it has been supposed to be 

 muscular. They may be either almost completely or completely retracted, 

 and then there is either no trace visible of them or they are visible as 

 clear lines converging towards the centre of the body 2 . They are said to 

 perforate the cuticle, but it is possible that the latter may be excessively 

 attenuated and extend over them. As to number, Rhynchaeta Cyclopum 

 has one suctorial tentacle of great mobility ; Urnula Epistylidis one which 

 may be branched ; but there are usually a number, either scattered over the 

 body, confined to the anterior surface, or grouped in two or more bundles. 

 The following are peculiar. Dendrocometes has 4-6 arms radiating from 

 the body, each arm branched terminally, and each branch ending in a 

 number of short points with retractile tips. A tube is said to commence at 



1 See Maupas' account of the act in Sphaerophyra magna, A. Z. Expt. ix. 1881, p. 302-3. 



2 This persistence of the retracted tentacles is difficult to explain : it is well established in some 

 instances, e. g. Hemiophrya gemmipara ; but in others, e. g. Sphaerophrya magna, Acineta fetida, it 

 does not occur, and the tentacles are processes of the peripheral zone of protoplasm (Maupas). It is 

 possible that just as the protoplasm of the prey passes into the body in a stream continuing the axis 

 of the tentacle, so the substance of the tentacles themselves may, owing to differentiation, follow the 

 same path. See on the subject, Fraipont, Bull. Acad. Roy. Beige, xiv. 1878, p. 490; and for views 

 for and against the resemblance of the tentacles to pseudopodia, see Id. ibid. p. 489 ; Maupas, A. Z. 

 Expt. ix. 1 88 1, p. 353-9. 



