34 D. KEILIN 
larger specimens, even with the naked eye. It is richly vas- 
cularized and its surface is irregular and lobulated. In longi- 
tudinal median section the pharyngeal bulb is seen to be 
composed of the three following portions: (1) an external 
epithelial sheath, (2) a median mass of musculo-vascular tissue, 
and (8) an internal portion composed of aggregates of deeply- 
staining cells. 
Almost all zoologists who have dealt with the anatomy 
of earthworms have given more or less attention to this 
organ, but, unfortunately, their opmions as to the nature 
and function of the deeply-staming cellular aggregates are 
either unsupported by observations or contradictory. I do 
not intend to give here a complete account of the previous work 
on this subject, as this has already been done by Vejdovsky 
(1884, pp. 101-6) and Stephenson (1917, pp. 253-60). I shall 
therefore confine myself to a brief mdication of the main 
views held on this subject by previous authors, classifying them 
under the four following groups : 
(1) Several authors, without paying special attention to the 
structure of the pharyngeal bulb, accorded to it the function of 
a salivary gland ; in this category come the observations of Leo 
(1820) and Clarke (1856) (cited by Vejdovsky), Lankester (1864, 
p-. 264), Vogt and Yung (1888, pp. 461-3), and Beddard (1895). 
(2) Vejdovsky (1884, pp. 101-6), Willem and Minn (1899), 
de Ribeaucourt (1900, pp. 246-7), and others, succeeded in 
tracing ducts which led from the deeply-staining cellular 
ageregates, through the muscular portion, but, although they 
could not detect any continuity of these ducts with the pharyn- 
veal lumen, they nevertheless accorded to these cells a secretory 
function similar to that of a salivary gland. 
(3) Michaelsen (1886, cited by Hesse), Hesse (1894, pp. 10-12 
and Pl. 1, fig. 24), and especially Eisen (1894-6), found the 
ducts of the deeply-stainmg gland cells to pass through the 
muscular portion, penetrating between the cells of the pharyn- 
geal epithelium and opening into the pharyngeal lumen. 
(4) Finally, Stephenson (1917) completely denied the existence 
of any communication between the deeply-staiing cells, which 
