356 LEWIS HENRY OOUGH. 



one or two processes towards the cuticula to subcuticular 

 muscles, and also one or two processes into the depth of 

 the scolex to connect with the nerves (fig. 28). The nucleus 

 is large, round, measuring 5^* in diameter; it contains a 

 nucleolus and a few chromatin bodies. The plasma is fibrillar 

 in appearance, several fibrillte uniting to form the processes 

 leading to the subcuticular muscles or to the nerves. The 

 whole cell has much more resemblance to a nerve-element 

 than to a myoblast ; it differs from the myoblasts of the paren- 

 chyma muscles in the obvious connection with the central 

 nervous system, in being connected to more than one muscle- 

 fibre, and in being multipolar instead of bipolar. 



Young (1908) finds that the " Sommer-Landois " cells 

 orio-inate from cells similar to those I have described as 

 occurring in the dorso-ventral muscle, and he lays importance 

 on the fact that the muscles are present before the " myoblast" 

 differentiates. The nerve-connection was observed already 

 by Zernecke (1908) and Blochmann (1896) before Young. I 

 consider Young to have been quite justified in giving the 

 name ''neuro-muscular cell" to the Sommei'-Landois cells, as 

 the cells are certainly quite as much nerve-elements as muscle- 

 elements. 



The Muscles of the Suckers. — It is possible to distin- 

 guish between parenchyma and subcuticular muscles in the 

 suckers in the same way as in the rest of the body, the 

 myoblasts and " neuro-muscular " or " Sommer-Landois " 

 cells giving the clue to the group to which the muscles 

 belong. 



The radial fibres belong to the parenchyma muscles, the 

 muscles just under the cuticula running pai*allel to the cuti- 

 cula to the subcuticular muscles. 



In Avitellina the radial muscles have lost their myoblasts, 

 but in other forms examined by me (Tasnia, Dipylidium, 

 Cittotfonia) it has been possible to readily demonstrate 

 the presence of lateral myoblasts. 



In Avitellina centripunctata (Eivolta), and in Ano- 

 plocephala magna (Abilgaard), there is a layer of cells 



