TAPE-AVOEMS OP THE SUB-FAMILY AVPl'ELLINIX.i:. 853 



number of fibres in a bundle and the number of bundles have 

 remained the same, and if we were to judge entirely by- 

 transverse sections, we would have to conclude that the 

 number of fibres in a bundle and the number of bundles is 

 constant. 



The fibres of the longitudinal muscle are apparently- 

 arranged in bundles of about twenty-four, with a few 

 solitary muscles scattered near the subcuticula. 



The subcuticular muscles arise, according to the usual view 



Text-fig. 6. 



I 



I 



a.- 



1.2.3.4. 5.6.7 8 9 10 II 12 13. 14.15.1 6. 17 



The figure represents; a modification of the arrangement of the 

 muscle-fibres shown in Text-fig. 5. The ai-rangement in 

 bundles, as seen in transverse section, is only apparent. 



as products of the " Sommer-Landois " cells, which are sup- 

 posed to be myoblasts. Young (1908) opposes this view, as 

 he finds the subcuticular muscles already formed before the 

 " Sommer-Landois " cells are differentiated. Young con- 

 sequently refuses to apply the term "myoblast" to them, 

 and calls them " neuro-muscular " cells, because they send 

 fibrillar processes into the muscles and because they are also 

 connected with the nerves. 



The "Sommer-Landois" cells of Avitellina are best 

 examined in sections throug-h the scolex. These cells send 



