794 PROFESSOR J. STEPHENSON ON 



Hesionid^. 



Castalia punctata. 



A considerable number of specimens were examined. It may be noted that the 

 intestine is, considering the small size of these animals, remarkably opaque ; and in 

 most specimens it is only in a few segments at the posterior end that the intestinal 

 canal is sutHciently transparent to allow ciliary motion, if present within it, to be dis- 

 tinguished. Nevertheless the appearances are often striking. 



In specimens examined under a coverslip, the anus is often seen to be closed ; the 

 posterior part of the intestine may also be contracted, and its lumen obliterated ; and 

 in such cases ciliary action is of course absent. During the examination, however, the 

 anus may be seen suddenly to open, and the intestine to dilate ; a violent ascending 

 ciliary action then becomes visible in the hinder intestine, beginning at the anus and 

 extending upwards till obscured by the opacity of the intestinal wall. 



In some cases the anus may be open, and the ascending ciliary action may be 

 observed, throughout the examination ; while in others the anus may be closed and 

 ciliary action absent. Sometimes even with the anus closed, ascending ciliary action 

 may be seen within the intestine in one or two segments at its hinder end. In one 

 case the ciliary action was downwards, towards the anus, in the last four segments, 

 while above this it was in the reverse direction for the small distance — about two 

 segments — which intervened before the intestine became too opaque to allow of 

 observation. 



The above paragraphs recapitulate observations made at Plymouth. In a number 

 of Hesionids examined at Millport, which were probably also specimens of Castalia 

 punctata, exactly similar phenomena were observed ; — violent reversed ciliary action 

 with open anus, visible as far as the intestinal wall was transparent ; a fainter ciliary 

 motion, near the anus only, when the anus was closed. Small particles were seen to be 

 drawn to the anus and taken into the intestine. In each of two specimens examined, 

 a string of yellowish mucus was seen to be passed out without interruption of the ciliary 

 action ; in one case part of this string was drawn in again, apparently through its 

 getting towards the side of the anal aperture and so coming within the action of the 

 ciliary current {cf. ante, p. 744). 



Antiperistaltic contractions of the intestine are also to be observed, but are very 

 variable. They may be absent altogether ; or a few irregular antiperistaltic waves, of 

 moderate amplitude, may be seen beginning at the anus or sometimes further forwards ; 

 these pass over a few segments and then cease. In one specimen antiperistalsis was 

 observed to occur throughout the greater part of the leiigth of the body ; the contrac- 

 tions were, however, irregular and intermittent, and afterwards subsided altogether. 



In no case was any connection observed between the antiperistaltic waves of the 

 intestine and the contractions of the dorsal vessel, 



