(Esophageal Teeth of the Stroiuateidiie. 



2')! 



attached to its centre was one of the tooth-like processes 

 which line the interior of each sac, and it was at first supposed 

 that the placoid nature of the teeth was thus evident. On 

 furtlier examination, however, no lines of growth wore seen 

 in the scale, it was unaffected by acid, and, on boiling in 

 caustic potash, it was seen to bo niado up of a somewhat 



Fiir. 1. 



ITTiTn. 



One of the tooth-like processes of the oesophageal sacs of 

 Psenes natalensis. 



reticulate fibrous slieet of clear liorny-looking tissue. Towards 

 tlie peripliery this substance was liomogeneous, and near the 

 centre fibres could be seen passing upwards to form the long 

 " tooth " (text-fig. 1). On its ui)i)er two-thirds there were 

 short offshoots, each capped with a hollow, sharp, curved 

 spine, the longest being about "33 mm. Thev thus differ 



17^ 



