MORPHOLOGY OF MBLIBE 531 



the ground substance (hyaloplasm or sarcoplasm) of the inner 

 region shows less affinity for cytoplasmic stain than that of the 

 outer region. The granules (macromeres) of the inner region 

 are farther apart than those (micromeres) of the outer region 

 of the muscle-fibre. This is perhaps also the reason why 

 the muscle-cell of molluscs appears as being, according to 

 Schneider, ' innerhalb einer geringen Sarcmenge '. Chromatin 

 bodies are distributed throughout the nucleus, either in the 

 meshes of the linin and around the nuclear periphery, or 

 around the peripheral part only (figs. 33, K, 82, Kar). The 

 peripheral granular net (sarcolemma ?) may be seen, in the 

 whole mounts of muscle-fibres stained by Congo red, as a fine 

 granular structure around the periphery of the fibre (PI. 31 

 fig. 32). 



The structure of the inner body-wall as found beneath the 

 basket formation (PI. 27, fig. 3) of the muscle arrangement in 

 the body-wall, shows apparently no regular arrangement of 

 fibres as in the case of the muscles ; the fibres here, which are 

 of connective tissue, seem to extend in every conceivable 

 direction (PI. 27, fig. 5), and this layer is continuous until some 

 visceral organ or the pericardial chamber is reached. In this 

 plexus of irregularly arranged connective-tissue fibres and cells 

 are the visceral bodies : the brain, the heart, the stomach, the 

 intestine, the organs of reproduction with their adjuncts, and 

 the renal organs. The amount of connective tissue in the body- 

 wall does not render it opaque. This is partly due to the loose 

 arrangement of the various kinds of tissues and to the presence 

 of numerous sinuses (PI. 31, fig. 31, Sp) containing a transparent 

 fluid. This fluid contains characteristic, primitive connective 

 tissue cells and strands (PI. 31. fig. 34. Pnc). 



5. The Visceral C a v i t y . 



According to Lang (1H96: 211) the Mollusc a are said 

 to have primary and secondary body-cavities. The former is 

 the system of lacunae and sinuses, into which the arteries 

 open, and out of which the veins, where these are present, 

 draw their blood. It has no epithelial walls of its own. Its 



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