788 PROFESSOR J. STEPHENSON ON 



note his reference to the fact that Spengel found in Oligognathus and other Eunicidge a 

 tube which apparently ends blindly behind, and anteriorly opens further forwards than 

 the " Nebendarm " of Capitellids, at the anterior end of the jaw-sac ; it differs also in 

 having no muscularis. In larval Eunicidse Kleinenberg found both anterior and 

 posterior openings into the gut. In general, the accessory gut appears to be a separated 

 neural intestinal groove ; the separation may be more or less complete, various stages 

 being exemplified in the various genera of the Capitellidre. Its occurrence in two 

 femilies so widely separated as the Eunicidse and Capitellidse shows that it is an 

 essential feature of Annelid organisation (dass in ihm ein dem Annelidentypus in- 

 harentes Organ vorliegt), a view to which we are forced also by the recognition of 

 homologues of the " Nebendarm " in other groups ; as such may be mentioned the noto- 

 chord (Ehlers), the accessory intestine of Gephyrea, and the similar structure in 

 Echinoderms (Eisig). 



On the subject of intestinal respiration in general, Eisig repeats his former views 

 (;vide supra). In a large number of Annelids the chief part of the respiratory function is 

 performed by the intestinal wall, and this is especially the case in those forms which 

 are without specific respiratory organs. In such there may actually be a collection of 

 gas (oxygen) in the intestine ; and in some, even special reservoirs (so-called swim- 

 bladder-like organs) may be formed to contain it. In many Annelids, again, the 

 separation of the nutritive ;ind respiratory activities of the gut has been secured by the 

 provision of a deep groove, with an ascending ciliary current, in the posterior portion 

 of the intestine ; this groove may extend along the whole of the intestine, or may be 

 separated from the main channel as a " Nebendarm." Hence the latter arrangement is 

 to be considered as a means of bringing water destined for respiratory use to the 

 oesophagus without interfering with digestion and absorption ; and this is especially to 

 be seen in the gill-less Capitella, where there is also an oesophageal groove. No other 

 function has been assigned to the accessory gut of Annelids and Gephyrea ; Agassiz, 

 however (without adducing any evidence), supposed that of Echinoderms to be excretory, 

 though Perkier, probably rightly, considers it to be respiratory. 



Lastly, Eisig, rejecting the division of the Chsetopoda into Polychseta and Oligochseta, 

 considers the Capitellids as closely related to 01igocha>te forms, and endeavours to 

 explain the absence of the accessory gut in Oligochaeta. In the terrestrial Oligochseta 

 its absence is of course comprehensible. As to aquatic forms ; — if it were to be 

 shown that these represented the more primitive Oligocliasta, it would be difficult 

 to understand why they, so closely related to the Capitellids;, have dispensed with 

 a "Nebendarm"; especially as they have to rely (except Alma nilotica) entirely 

 on cutaneous and intestinal respiration. But marine Oligochfeta are descended 

 from terrestrial forms ; and it is possible that the same applies to the freshwater 

 Oligochaita too. 



In Eisig's account of the physiology of the accessory gut, and in his theoretical 

 conclusions presented, though in a much compressed form, above, there are many points 



