300 A. T. MASTEEMAN. 



Proctodseum^ Stomodseum, and Subneural Gland. 



From a want of definite knowledge upon the point one 

 cannot speak of a proctodseum with any degree of certainty, 

 but Caldwell refers to a " slight invagination of ectoderm '' in 

 the formation of the anus. From a figure of an early stage, 

 given by MetsclinikofF (14), there can be little doubt that the 

 organ usually referred to as the oesophagus is epiblastic in its 

 origin. In Metschnikoff^s figure (14, Taf. xix, 1) the connection 

 between the a3sophagus and stomach is apparently not yet 

 established. In view, however, of no certain statement, the 

 (Esophagus will be described later. 



Subneural Gland. — There remains an important organ 

 about the origin of which there can be no doubt. During 



3. 3. 4. 



1. Early stage of subneural gland in longitudinal section. 2. Later ditto. 3. Later 



than 2. 4. Latest stage ditto. 



development the epiblast becomes tucked in at the mouth, and 

 in the mid-ventral line of the hood, anterior to the mouth, there 

 is formed a small depression (woodcut I). As the depression 

 deepens and increases in size it is carried further inside the 

 buccal cavity (see woodcuts 2, 3, and 4), until the latest con- 

 dition I have observed, seen in PI. 21, fig. 38, s. %., is arrived at. 

 In median sagittal section the same organ is shown in PI. 20, 

 fig. 20(5. n.). Its walls at this stage still exhibit a structure 

 closely similar to that of the oesophagus. As referred to below, 

 this may be termed the subneural gland, and may be compared 

 to the organ of the Tunicata bearing the same name, and 



