780 PROFESSOR J. STEPHENSON ON 



necessarily be the absorption of oxygen (and dissolved food-matters) by the intestinal 

 epithelium. 



I cannot find that any evidence against the respiratory nature of the phenomenon 

 is adduced ; there would therefore seem to be no reason to doubt that the antiperistaltic 

 contractions have at the present day the double function of moving in a forward 

 direction both the blood in the network and the fluid in the alimentary canal. 



(4) (Thesis 21). — "Die antiperistaltische Bewegung der Muskelwand des Darmblut- 

 sinus (der visceralen Muskelschicht der Gonocolsacke), die sich in die von hinten nach vorn 

 verlaufende Kontraktionswelle des Riickengefasses fortpflanzt, welches selbst nur eine 

 vordere mediodorsale Fortsetzung des Blutsinus ist, hatte vielleicht urspriinglich den Sinn, 

 die im resorbierenden hinteren Abschnitt des Darmes gewonnene ernahrende Fllissigkeit 

 auch dera vorderen Korperteile zu gute kommen zu lassen. Das innere Flimmerkleid 

 des Darmes besorgte allein die analwarts gerichtete Fortbewegung des Darminhaltes." 



In Thesis 20 {vide supra) the statement was made that (in the Polychseta) the sole 

 function of the antiperistaltic contractions is circulatory. Here it is stated that this is 

 perhaps also their original function (" • • • hatte vielleicht urspriinglich den Sinn . . . "). 

 This is, of course, opposed to the general argument of the present paper, according to 

 which the antiperistaltic contractions are an original property of the alimentary canal 

 subserving ingestion, and only secondarily brought into the service of the circulation. 



In the first place, it will be agreed that peristalsis, in whichever direction it proceeds, 

 has throughout the animal kingdom, speaking generally, the function of moving matters 

 contained in the lumen of the tube, not in the substance of its wall. 



In the second place, peristalsis (under which head I include for present purposes 

 antiperistalsis) is known at lower levels in the animal kingdom than the Annelida. It 

 occurs, for example, in the oesophageal tube of Actinozoa ; thus Carlgren (11) describes 

 how ingestion is mainly accomplished by peristalsis in Tealia, Actiyiostola, and Bolocera, 

 and is partly eff"ected by the same means, with the help of ciliary action, in Caryo- 

 phyllia ; peristaltic action is also said possibly to assist in the expulsion of solid food- 

 remains in Tealia and Actinostqla. Again Lang (28) describes in Poly clad Turbellaria 

 a series of sphincter-like bands of muscular tissue on the branches of the alimentary 

 canal, which can contract so far as to obliterate the lumen ; by means of peristaltic-like 

 contractions of these bands the fluid contents of the main channel of the alimentary 

 canal are driven throughout the system as far as the end branches, and afterwards back 

 into the main tube again. 



Arguing from the comparative standpoint, therefore, it would seem that the original 

 function of peristaltic contractions in the animal kingdom was to move in one direction 

 or other substances contained within a tube-like cavity.* 



* It is perhaps rather disingenuous on my part to introduce the Polyclada as an example drawn from a lower 

 phylogenelic level, seeing that I am doubtful about accepting Lang's theory of the derivation of Annelids from Tur- 

 bellarian ancestors ; I am not sure that there is not more truth in Hubrecht's view, which is the reverse of Lang's. 

 Lang, however, and those who think with him, will appreciate the force of the example in this connection, even if it 

 does not appeal so strongly to me. In any case, there remains the fact that peristalsis occurs amongst the Ca'lenterata. 



