APPENDIX III 299 



the openings above the ventral cord into the Umbs, to 

 find its way back to the heart after passing through the 

 gills, the rest continues posteriorly, bathing the intestinal 

 canal (the hind-gut) to find its way, by some means which 

 is not yet clear, into the dermal sinus which, in the 

 posterior part of the body, is continued right round the 

 body, there being no dissepiments and no separate cardial 

 sinus. It then flows forwards till the first lateral dissepi- 

 ment confines it to the dorsal channel which contains the 

 heart and forms the cardial sinus. How the blood finds 

 its way from the intestinal to the dermal sinus in this 

 posterior part of the body we have not been able to ascer- 

 tain. A longitudinal dissepiment runs right along each 

 cercopod or anal cirrus, which shows that the blood flows 

 along one side and back by the other. We may also per- 

 haps assume that under the two rudimentary cirri openings 

 occur corresponding with the communication which once 

 existed at the tips of the cirri which they represent. These 

 are however probably not the only openings between the 

 two sinuses. We have not been able to make out the 

 relation of the circulation to the rudimentary limbs ; sec- 

 tions of the rudimentary gills seem to show that they are 

 functional as such. 



We have seen that special muscles probably regulate the 

 flow of the blood out of the intestinal sinus into the neural 

 sinus (if it can be so called), on its way to the fimbs. There 

 can be no doubt that the dorso-ventral muscle-bands play a 

 part in propelling the blood through the sinus. The intes- 

 tinal musculature, except in the hind-gut, is too weakly 

 developed to assist much. But it is easy to see how, in 

 such a tubular sinus, the movements of the intestinal canal 

 running along its centre could materially help the circula- 

 tion of the fluid between them. 



We had no means of following the course of the blood 



