524 DR MASTERMAN ON THE FURTHER ANATOMY AND 



interpretation of this organ as the heart were accepted, and I have every reason to 

 believe that such cannot be demonstrated. 



In the discussion upon these points between this author and myself, we have been 

 blamed for complicating the points at issue by each using a different nomenclature, so I 

 may be excused for giving the following table illustrating the two views : — 



1. " Sub-neural gland," = Harmer's " notochord." 



2. " Sub-neural sinus," = ,, " proboscis- vesicle." 



3. " Pre-oral sac," * heart." 



Hakmer accepts the presence of my " dorsal blood-sinus," and believes that it will be 

 proved to communicate with (3) and not with (2) ; and, on the other hand, he denies the 

 communication of (3) with the pre-oral ccelome. 



Whilst denying my interpretation of the " paired notochords," Harmer corroborate* 

 my description of them, and, apparently, of the other leading anatomical points in my 

 work not mentioned above. 



It appears to me that the disputed points will have to be settled by a renewed 

 investigation of the development of Balanoglossus. Should the proboscis-vesicle of 

 Balanoglossus be indubitably proved to arise from mesenchyme or from the proboscis 

 ccelome, then it is possible that the pre-oral sac above described may represent, in 

 Cephalodiscus, the more primitive condition of the homologous structure, whereas, 

 should the proboscis-vesicle prove to be developed from ectoderm, it would probably 

 have, as formerly suggested (6), to be regarded as the distal extremity of the sub-neural 

 gland. 



In any case, a rhythmically pulsating organ with an internal cavity, completely 

 closed, is so anomalous a structure that more knowledge of its structure and develop- 

 ment is very essential. It seems possible that the proboscis-vesicle of Balanoglossus 

 may yet be proved to communicate with the pre-oral ccelome by minute lateral apertures 

 in a similar manner to the pre-oral sac in Cephalodiscus. The radiating cells above 

 described would then represent the proboscis gland (cf. larval nephridia of Annelida), 

 and the resemblance of proboscis-vesicle and pre-oral sac would be very close, both 

 functioning as contractile vesicles for the expulsion of excretory fluids into the pre-oral 

 ccelome. 



Summary. 



The following is a brief summary of the chief features dealt with in the fore- 

 going :— 



(1) The pharynx has special adaptations for the separation of food and water- 

 currents, amongst which may be reckoned hyper- and hypo-pharyngeal 



*■ Prior to this, the organ here referred to ha3 been unnamed ; the above name may be suggested for adoption in that 

 it is descriptive without in any way implying a special homology. 



