CILIA. 



615 



within the tentacula, were moved in two diffe- 

 rent directions, namely, from the base to the 

 point, and from the point to the base ; and 

 (supposing the arm spread out horizontally,) 

 the outward current was along the under part 

 of the tube, and the returning one along the 

 upper: (see A.) I also observed these internal 

 currents of the tentacula in a young specimen of 

 Actinia senilis, which seemed to have been very 

 recently discharged from the parent ; in it also 

 there were radiating currents on the disc, but 

 they stopped at the base of the tentacula. 

 Thus the external currents on the disc and ten- 

 tacula were found in one species, and they 

 occur on the disc in some other species in the 

 young state, but their occurrence in this situa- 

 tion is by no means general in adult Actiniae. 



The phenomena described are in all proba- 

 bility connected with the processes of nutri- 

 tion and respiration. They bear a striking 

 analogy to those I have observed in the Echino- 

 dermata. 



The ova of the Actiniae were observed by 

 Rathke to revolve round their axis, and occa- 

 sionally to move straightforwards in the 

 water. He could detect no cilia or other 

 moving organs.* 



6. Echinodermata. The animals of this 

 class in which I have observed the ciliary 

 motion, are different species of the Sea-star 

 (Asterias), and the Sea-urchin (Echinus). In 

 proceeding to describe the phenomena in the 

 Asterias, I must first take the liberty of ex- 

 plaining some points in the anatomy of that 

 animal, referring the reader for other details to 

 the proper sources, especially the monograph 

 of Tiedemann.-f 



On the under surface of the Asterias, (I 

 speak of the Asterias rubens in particular, 

 Jig. 298, A, B, C, as it is a large species and' 

 common on our shores,) we observe the mouth 

 in the centre, and the tubular feet (I, Jig. B) 

 projecting in rows along the under part of the 

 rays. Nearly the whole surface of the animal 

 is beset with three kinds of eminences. First, 

 hard calcareous processes, (a, jig. C,) placed 

 like studs at some distance from each other. 

 Secondly, claw-like processes (6, 6) ; these sin- 

 gular organs are more thickly set ; they consist 

 of a solid stem of soft substance, bearing at the 

 extremity a sort of pincers or forceps of hard 

 calcareous matter, like the claw of a crab. 

 They resemble analogous organs found on the 

 Sea-urchin, only that the maxillae or pincers in 

 the latter consist of three pieces ; they were 

 named antennae or feelers by Monro, but Miil- 

 ler regarded them as parasitical animals. The 

 third sort of processes (c, c,) are named the 

 respiratory tubes, and are the most important 

 in regard to our present subject. They are 

 short, conical, membranous tubes, communi- 

 cating at their base with the internal cavity of 

 the body, and perforated at their point by an 

 orifice which can be very perfectly closed. 

 Most of them are placed in groups or patches, 

 and, corresponding with each group of tubes, 

 the fibrous membrane forming the wall of the 

 body presents on its inside a pit or shallow 

 depression (e\ perforated with holes, through 

 which the tubes communicate with the general 

 cavity. Like the tentacula of the Actiniae, 

 which they resemble in several other respects, 

 they can be distended with water and elon- 

 gated, or emptied, contracted, and shortened. 



Fig. 298. 



C 





A, Asterias viewed from above. B, Cross section of a Ray. C, Part of the section at m, fig. A, magnified. 



The cilia 



' Dorpater Jahrbuch. fiir Litt. Stat. und Kunst. Dalyell, who had long before observed it. 

 Bd. i. Heft. i. p. 8486, quoted by Purkinje and could be distinctly perceived. 

 Valentin, p. 32. I have since seen the indepen- f Anatomic der Rbhren Holothurie, &c. Land- 



dent motion of the ova when extracted from the 

 animal. It was shown to me by Mr. Graham 



shut, 1816. 



