178 OLIGOCHAETA 



in three species it is turned into a beautiful violet by the action of alkali ; it 

 is dissolved out and destroyed by alcohol^. Colourless gland-cells appear to be 

 particularly abundant in A. variegatuvi, and to be the only ones present in A. niveum. 

 There can be no doubt that the coloured (and colourless) oil-globules form the contents 

 of cells similar to those found in the epidermis of the Oligochaeta. Leidy (6), it is 

 true, has spoken of them as nuclei either of the hexagonal cells of the prostomium 

 or of the muscle-fibres of the body-wall ; but this is undoubtedly an incorrect opinion. 

 The cells, however, which contain these bodies have, according to Vejdovsky, no 

 nuclei ; so far as regards A. heviprichii I have been able (32) to confirm him, but not 

 as regards A. tenehrarum (74), where the nuclei are not difficult to see. However, 

 they are present in the developing cells of A. heynprichii; in such cells the coloured 

 body first appears as a minute droplet, which gradually grows, pushing the nucleus 

 to one side ; the nucleus seems to be itself converted into oil (Vejdovsky). 



The muscular layer of the body-wall is very delicate. Leidt (6, PI. ii. figs. 8, 9, 

 12) figured a single layer only of circular fibres. Vejdovsky with difficulty, and then 

 only occasionally, detected a delicate circular layer of fibres ; the longitudinal layer 

 also exists, and I have figured both in A. headleyi (68, PI- xii. fig. 2 m, m'). 

 Aeoloaoma is therefore in this respect a typical Oligochaet. The coelom is not 

 divided by intersegmental septa into a series of segments ; one segment only, the 

 first, is bounded by a distinct septum. Nevertheless, the body-cavity is traversed 

 by muscular fibres which extend between the alimentary tract and the parietes ; 

 and serve to keep the former in position. This statement applies no less to 

 'A. quaternarnwi and hemprichii than to other species. The fibres in question 

 are nucleated, the nucleus lying in an oval ^welling of the fibre at about its 

 middle. They have been figured by Vejdovsky (24) and by myself (68). In 

 the cavity of the prostomium, and in the section of the body-cavity round the 

 pharynx, they are more numerous and closely set than elsewhere. There is 

 occasionally a branching and anastomosis of the individual fibres. Similar uni- 

 cellular muscular fibres (Beddard 68, PI. xii. fig. 3) are attached to the sacs of 

 the setae, and serve to move them ; it is interesting to find that the muscles which 

 connect together the seta-bundles of the same segment are histologically different; 

 these strands (Beddaed 68, PI. xii. fig. 3 sm) consist of exceedingly fine fibrils, closely 

 set together, and with no visible nuclei. These latter muscles appear to be absent 



are really symbiotic algae ; he observed them dividing. I believe that I have shown (74) that it is 

 not chlorophyll. 



' In ^. tenebrarum a solution of iodine produces a remarkable effect ; a dense black colouration spreads 

 over the outside of the oil-globule, which as rapidly disappears ; this effect was only seen in living cells. For 

 further remarks on the pigment of Acolosoina I may refer to my two paper.% upon the subject (Nos. 32, 74). 



