On the Structiire and Development of Avgiope. 501 



the perìpheral caual a brauch passes off into each tentaele. The mass 

 of the lophophoi-e consists of a homogeneons , clear, snppoi'ting- siib- 

 stance which is also found g-reatly developed in the stalk , at the origin 

 and Insertion of the muscles, and in other parts of the body wall. A 

 few granular cells are fonnd in this substance. The membrane which 

 is formed of this homogeneous material is covered within and without 

 by a layer of fiat epithelìnm cells. Fig. 13 represents a transverse sectlon 

 through a tentaele and fig. 15 a longitudinal section through the base 

 of another, showing the ciliated groove, formed by the lip and the ten- 

 taele, and the attachment of the lophophore to the mantle. Froni these 

 figures it is seen that the greater part of the tubulär tentaele is composed 

 of the homogeneous supporting substance ; lining this internally is a 

 layer of fiat epithelium cells. In the canal a number of muscular fibres 

 (fig. 13 and 15 mf] are seen in section, these lie chiefly onthat side of 

 the tube which is nearest the centre of the lophophore. The supporting 

 substance is covered outside also with a layer of epithelium which on one 

 side is fiat and non-ciliated, on the other three sides very high and ciliated. 

 These latter sides are the inner and the two lateral. At the base of the 

 tentacles on the inner side the columnar epithelium becomes very high 

 and then becomes very low again, thus an epithelium cushion is formed, 

 which is continuous ali round the ciliated groove on the outer side. The 

 remaining epithelium of the groove is cubical and ciliated except just 

 at the edge of the lip where again it becomes very high. The other side 

 of the lip is covered with non-ciliated cubical cells which gradually pass 

 into the fiat epithelium covering the disk of the lophophore. In the living 

 animai the cilia can easily be seen in motion ; those at the base between 

 each tentaele are particularly large and powerful . It will be seen that this 

 arrangement of cilia is adapted to bring any floating particles of food 

 into the ciliated groove and when once there, they are no doubt driven 

 by the action of the cilia towards the mouth, which as is stated above 

 opens into this groove. I bave been unable to detect any blood corpus- 

 cles in the tentacles, and I believe the sole function of the lophophore 

 Ì8 to set up a stream by means of its cilia, and so to bring diatoms and 

 other articles of food to the mouth , and that it has no respiratory func- 

 tion whatever. Indeed it is difficult to imagine how an interchange 

 of gas could take place through the thick , dense layer of supporting 

 substance. 



The Protrusion of the tentacles is probably brought about by for- 

 cing in a perivisceral fluid, but their retraction and coiling movements are 

 probably occasioned by the muscular fibres which lie in their interior. 



Mittheiliingen a. d. Zoolog. Stiition zu Neapel. Bd. IV. li 3 



