163 
cells upon the stomach. Willem* finds on examining 
the cells in the fresh state that they contain oleim 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 
hemoglobin. The corpuscles are minute colourless 
rounded or ellipsoidal, nucleated cells ‘005 to ‘01 mm. 
(5 to 10u) in diameter. They are comparatively few in 
numbers and their origin is unknown. 
Heart anp Heart Bopy. 
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 
** Miscellanées Biologiques dédiées au Professor Alfred Giard, 
Station Zoologique de Wimereux, p. 556, Paris, 1899, 
