224 



W. HAROLD LEIGH-SHARPE 



Though pointing anteriorly, the sheath sac cannot be considered 

 as homologous with a pseudosiphon. 



Leading into the apopyle is a shallow cavity which appears to 

 be homologous neither with a siphon, nor with the cavity of 



r5 



o- 

 cirx. 



Fig. 3 Notidanus griseus. A transverse section through the party wall 

 between the cavity and the sheath sac, in the position indicated by the dotted 

 outline in figure 2 (haemalum - eosin) . Ej)., stratified epithelium; M., muscle. 



Fig. 4 Spinax niger. 1, 2, 3, 4, spines; H., hypopyle; S., siphon; Sm., sen- 

 ticetum; a., its apex. 



Chimaera. It offers a homology with the former as to situation, 

 confirmed by its being a sac with muscular walls capable of 

 fulfilling the normal functions of a siphon. 



A portion of the thin partition between this cavity and the 

 external sheath sac, from the area bounded by the dotted outline 

 in figure 2, was removed and sectioned, with the result that it 



