OPHIDIAN TAPEWORMS, 



167 



beginning of the formation of the ducts passing between the two 

 water-vascular tubes. 



Text-fig. 38. 



7^\ m. 



w. V. 



Transverse sections tLrough portions of proglottids of Ichthyotcenia sp. 

 'M. Medulla, iv.v. Water-vascular tubes. 



I have, however, a few remarks to add to Schwarz's description 

 of this worm. This author does not mention the fact that the 

 neck region, at any rate just behind the scolex, is provided with a 

 very thick layer of longitudinal muscle fibres occupying the whole 

 of the space between the subcuticular layer and the medullary 



