NOTES ON HISTOLOGY OF LINGULA ANATINA. 6 



spherical in form, measuring 10-20,« in diameter. It is usually 

 depressed in one or two places. In section, therefore, it gives a 

 crescent or biconvex shape. Just within the wall of the corpuscle 

 there is a small refractive spherule, which is probably a nutritive 

 oil drop (PI. I., Fig. 2, r. g.). Treated with acidulated methyl 

 green it swells up and appears like a hollow sphere (PI. I., 

 Fig, 2), for the cytoplasm is very transparent and is consequently 

 invisible. When a section of blood corpuscles is stained with 

 erythrosin the cytoplasm stains homogeneously red in well fixed 

 specimens and looks rather compact. But under certain conditions 

 of precipitation by the action of some fixing reagents the entire 

 cytoplasm breaks up into coarse granules (Schollen) which also 

 take a deep erythrosin stain. The nucleus is very compact, and 

 the stain intense and uniform. The blood corpuscle has a well 

 defined and rather thick membrane. 



When the mantle of a young specimen (4.5-10 mm. in shell 

 length) is examined under a low power, the circulation of cor- 

 puscles can be very clearly seen through the shell, as Semper 

 ('6i) has described. In every branch of the palliai sinus the 

 observer can make out two opposed currents of blood corpuscles, 

 although there is no septum which divides the sinus into two 

 canals. The non-existence of a septum can be demonstrated in 

 the living specimen, for it is seen that, when occasionally a 

 corpuscle goes astray, it is quickly caught up by the opposed 

 stream, as Francois ('91) observed at Numea. The presence 

 of the two currents is made possible by a low ridge (Epithelleis- 

 ten of Blochmann) which arises from the floor (next the shell) 

 of the palliai sinus. The mantle of a young living Lingula is a 

 good object for class demonstration of blood circulation. When 

 sections are studied the corpuscles are sometimes found crowded 



