274 LIONEL JAMES PIOTON. 



The Hue of demarcatiou between the central granular or 

 luedullary part of the organ and the external or cortical 

 tissue is fairly well defined^ and at some points a split between 

 the two occurs. This is usually crossed by branching and 

 highly granular trabeculse (fig. 5). Sometimes it is con- 

 siderably widened (fig. 2, y.), though in no case is there any 

 sign of blood within it. On the other hand, the heart-body is 

 frequently so folded as, in section, to show spaces surrounded 

 by a proper superficial cortical tissue, which contains blood 

 (fig. 2, X.) ; nevertheless it may be said that the blood never 

 penetrates the organ,i but only flows between its folds and 

 strands. 



Between all the granules occurring in the heart- body a 

 series of steps can be traced^ so that it would appear probable 

 that they represent diff'erent stages in some process which it 

 must be the chief function of the heart-body to carry on. An 

 examination of the shapes and properties of these granules 

 will help to throw some light on the nature of that process. 

 The methods used in this study, besides that of sections, were 

 teasing fresh tissue and also tissue that had been macerated in 

 Bela-Haller's fluid, tests of solubility in different reagents, 

 and various micro-chemical tests, such as those for iron, fat, 

 glycogen, chitin, and uric acid. 



lu the following description the granules are treated in the 

 order in which they appear to pass step by step into one 

 another. But whether the history indicated be in fact correct 

 must be left an open question. Certain unstainable refringent 

 bodies have been mentioned above as occurring in the medulla 

 of the heart-body, embedded in the groundwork (fig. 5, e) ; 

 they are not conspicuous, and are apt to be overlooked, but as 

 they increase in size a space appears around them, which 

 renders them very noticeable (/). This is the origin of the 

 spherical spaces so characteristic of the medulla. Under an 

 oil-immersion objective these bodies are seen to consist of a 



' Except in a few doubtful cases, where I have noticed iu sections a small 

 patch of what appears to be coagulated blood in a cavity in the medullary 

 tissue. 



