62 W. N. F. WOODLAND 



which the island is stained red and the rest of the cell-plasm 

 green), and the remainder of the cell is packed with con- 

 spicuous granules. The cell process grows out from one pole 

 of the cell and at first is packed with granules identical with 

 those in the cell, but at some distance from the cell the substance 

 of the fibres becomes longitudinally striated (the striations being 

 sinuous when the muscle is not fully extended) and much less 

 granular ; in other words, comes to resemble nmscle-substance 

 (PI. 4, fig. 24). Another and very significant fact to be men- 

 tioned concerning the fibres of the big muscle is that, in the 

 proboscis and for some distance below it, these fibres, at least 

 in many cases, run obliquely, as is proved by the fact that the 

 fibres are seen to be cut transversely or obliquely in longitu- 

 dinal sections cut parallel with the long axis. PI. 4, fig. 25 

 gives some indication in very diagrammatic form of the 

 general arrangement of the muscle-fibres and their connexion 

 with the anchor- cells — an arrangement also found in A . 

 f o 1 i a c e a and A. liguloidea and probably in A . magna. 

 What can be the function of this huge axial proboscis muscle ? 

 Its extraordinary size enables us at once to dismiss the idea 

 that it is simply the retractor muscle of the minute proboscis, 

 as supposed by Salensky ^ and other authors, especially in 

 view of the fact that a well-defined retractor muscle (indicated 

 in A. liguloidea by Janicki in his Text-fig. 9) already 

 exists. In no other worm do we find a proboscis, of the size 

 found in Amphilina, associated with a muscle (known to be 

 a retractor) of the dimensions just described. In Turbellaria 

 the small proboscis is always retracted by a small retractor 

 muscle consisting of short diverging fibres ; on the other hand, 

 when, as in the Nemertines, the retractor muscles are long, 



^ Salensky described the fibres of the proboscis muscle as originatmg 

 posteriorly in two halves from the lateral subcutaneous muscle-layer, 

 and naturally could offer no explanation of the presence of his ' problematic 

 cells '. Hein and Cohn both failed even to find the anchor-cells (the former 

 confusing them with the myoblasts and the latter assuming that they were 

 in ])art identical with his flame-cells and in i)art ' Kunstprodukte ' ! ) 

 though these cells can be easily seen under a magnification of 30 diameters 

 and less. 



