SEA-FISHERIES LABORATORY. 243 



cells upon the stomach. Willem* finds on examining 

 the cells in the fresh state that they contain olein and 

 acid urate of sodium (brown), the former substance being 

 probably of a nature of a nutritive reserve and the latter 

 an excretory product. 



The blood plasma is red, due to the presence of 

 haemoglobin. The corpuscles are minute colourless 

 rounded or ellipsoidal, nucleated cells -005 to "01 mm. 

 (5 to 10/a) in diameter. They are comparatively few in 

 numbers and their origin is unknown. 



Heart and Heart Body. 

 The hearts are a pair of contractile bulbs connecting 

 the gastric and ventral vessels. They are capable of 

 great dilation. The thin walled auricle is merely a 

 swelling on the gastric vessel. The ventricle has thicker 

 muscular walls and its cavity is, in adult specimens, in- 

 vaded by a " heart-body." In post-larval and young 

 specimens the heart contains no trace of this body, but 

 it has appeared in examples 65 mm. long (fig. 37). At 

 this stage of growth the ventricular wall consists of an 

 outer cubical peritoneal epithelium and an inner but in- 

 distinct endothelium between which muscular tissue is 

 barely recognisable. The cavity of the ventricle is, 

 however, invaded by processes which repeat the structure 

 of the ventricular wall and are probably invaginations of 

 it. Later on, as the muscular tissue develops in the wall, 

 fresh invaginations occur (fig. 39). In full grown speci- 

 mens each process of the heart body is seen to be composed 

 of a very delicate endothelium, a muscular layer and a 

 mass of cells, some granular and some glandular, either 

 forming a fairly definite lining to the invagination or 



* Miseellanees Biologiques dediees au Professor Alfred Giard. 

 Station Zoologique de Wimereux, p. 556. Paris, 1899. 



