724 A. T. MASTERMAN. 



Cephalodiscus is to be regarded as a degenerate ally of 

 Balanoglossus has not much to commend itself; the conse- 

 quent assumption that tiie former has lost numerous gill- 

 slits perforating its anatomy in all directions^ not to mention 

 numerous other organs, has no justification in fact. We may 

 with Lang (5) suppose that Cephalodiscus has undergone 

 certain important modifications due to a semi-sedentary habit, 

 but the assumption that its proximate ancestors had many 

 pharyngeal clefts and gonads has nothing to recommend it 

 but its necessity for Willey's theory. I would prefer to 

 regard Cephalodiscus as the more primitive form, as its 

 want of metameric segmentation and its primitive method 

 of feeding would imply (9). On this basis the " Eichel- 

 darm " of the Enteropneusta must be regai'ded as a glan- 

 dular specialisation of the anterior end of the pharynx, to 

 be termed the subneural gland, owing to its functions and 

 structural relationships. 



In Cephalodiscus its distal end often exhibits a com- 

 mencing degeneration into chordoid tissue (which, by its 

 development in Actinotrocha, is clearly an arrested form of 

 glandular epithelium), whilst it is still functionally active as 

 a gland. In Balanoglossus, with a specialised burrow- 

 ing habit, the original function has been largely lost (though 

 the "Eicheldarm" of Balanoglossus is unquestionably 

 glandular;, and the chordoid tissue with supporting funclion 

 becomes still more in evidence. The organ to which the 

 name of subneural gland was given iu Actinotrocha 

 occupies exactly the same position as in Cephalodiscus, 

 but as it is only embryonic its walls would hardly be expected 

 to be of a definitely glandular nature. 



The pericardial sac of Cephalodiscus and its contained 

 heart are so similar to the pericardium (Herzblasc) and 

 heart respectively of Balanoglossus, and so different from 

 any structures found elsewhere, that the homology need not 

 be insisted upon. In a similar manner the mutual relations 

 of the ectodermal pit, the pre-oral canals, the pericardial sac, 

 and the suirounding blood-sinuses speak for themselves. 



