432 University of California Publications in Zoology. t v L - G 



5. The acetabular portion of the nervous system is developed 

 in connection with the acetabular sense organs and with the 

 power of locomotion in a definite direction. It corresponds to the 

 " brain" of Turbellaria and to the anterior ganglionic commis- 

 sure in Trematoda. 



6. The rosette portion of the nervous system is developed in 

 connection with the development of a powerful posterior organ 

 of attachment, and is comparable to the posterior ring-commis- 

 sure in the posterior sucker of a heterocotylean trematode. 



7. The rosette of Gyrocotyle is in structure and function a 

 true scolex, and corresponds to that organ in merozoic cestodes. 

 This correspondence is strikingly shown in a comparison of the 

 nervous system of the rosette of Gyrocotyle and that of the scolex 

 of the merozoic cestodes. 



8. On the basis of this evidence from comparative morphology 

 and of other evidence previously adduced from the embryology 

 of merozoic cestodes, it is proposed to regard the cestode scolex 

 as a posteriorly situated organ of attachment, the "neck" or 

 growing region as the antepenult region corresponding to the 

 antepenult segment in annelids, and the proglottis as the inter- 

 mediate region of the body. The anterior extremity has com- 

 pletely disappeared, according to this view. 



9. The limiting-membrane in Gyrocotyle consists of a sur- 

 face layer, composed of delicate fibres in a homogeneous matrix, 

 and immediately beneath this a layer of transverse and a layer of 

 longitudinal muscle fibres, non-nucleated. These are connected 

 by fine processes with a layer of large cells lying in the paren- 

 chyma of the body, the subcuticular cells. Some at least of these 

 cells are to be regarded as myoblasts of the cuticular musculature. 

 There is no ground for regarding them as sunken epidermal cells. 

 There is no trace in any of the tissues of the body of an epithelial 

 layer of cells. The lining of the genital ducts is a meshwork of 

 fibres in a homogeneous matrix, with nuclei scattered through it. 

 This passes by gradual transition into the non-nucleated condition 

 described for the limiting membrane of the body. 



10. The muscle fibres of Gyrocotyle are all nucleated except 

 those of the cuticular musculature. The latter are attached by 



