462 DISCOVERY REPORTS 



From a morphological standpoint, one of the chief features of the blood system is 

 that, if the mechanism I have suggested is correct, circulation would still be possible 

 in complete absence of the heart. Thus blood is sucked into the pericardium indepen- 

 dently of the heart and would pass into the aorta whether the heart were there or not, 

 since the aortic valve is part of the pericardial floor, and is controlled by the pericardial 

 dilator. And, further, the presence of valves in the supraneural vessel would ensure 

 a one-way circulation in the absence of the heart with its ostia. This is significant from 

 the fact that, in certain groups of Ostracods, the heart is entirely absent. In these forms 

 it is possible that the pericardial floor and vessels may yet be present. 



GUT 



The labrum has already been described (p. 438). The labral glands will not be dealt 

 with, as they have been investigated so often before in other Cypridinids (Newton 

 Harvey, 191 9). 



The gut consists of a well-defined oesophagus, leading into a globular stomach, which 

 merges into an extremely short hind gut opening at the anus just in front of the caudal 

 furca. 



The oesophagus exhibits a typical structure. Its anterior wall is thickened and bulges 

 posteriorly, converting the lumen into a cavity, moon-shaped in section. The whole 

 oesophagus is lined by very thin chitin and the bulge on the anterior wall extends a 

 short distance into the stomach. The aortic muscles which extend down and attach 

 to the oesophagus have already been described. Outside these there is a series of 

 circular muscles and, in addition, various dilator muscles which run to the anterior 

 walls of the labrum. 



The stomach, as in most Cypridinids, has no hepatic outgrowths, but is completely 

 enveloped in a mass of tissue which I have called the gut parenchyma. It is obvious, 

 even from the small amount of material at my disposal, that this tissue varies con- 

 siderably, not only in its staining reaction, but in its bulk. In two of my specimens 

 it almost obliterates the body cavity, while in the specimen figured in Fig. 8 there is a 

 large blood space between it and the body wall. A description of the variation based on 

 my material would be of little use but, since it probably is an indication of food storage, 

 an investigation of this point will be interesting when further material is available. 



In Fig. 8 I have drawn a section which exhibits all the cellular elements to be found 

 in the gut and its parenchyma. The gut epithelium consists of a uniform layer of tall 

 columnar cells, the cytoplasm of which is heavily vacuolated. It is separated from the 

 parenchyma by a network of muscles but, as will be seen from the figure, this separation 

 is not very marked. There is no basement membrane as described by Liiders (1909, 

 p. 113) in Gigantocypris. The bases of the cells may even in places bulge through the 

 network, so that they interdigitate with the inner layer of gut parenchyma cells. This 

 agrees with Miiller's description of Gigmitocypris (1895, p. 159), where he describes 

 a "strukturlosen, starkgefalteten Membran" at the base of the gut epithelium. 



