THK ANATOMY OF SOALIBREGMA INFLATDM. 271 



between the two rami of each of the parapodia of Eumeuia 

 longisetosa, but he did not I'ecognise the nature of these 

 papillae. 



Our knowledge of lateral sense organs of this kind is due 

 almost entirely to Eisig, who has described their relations 

 and structure in his monograph of the Cnpitellidge (1887). 



The lateral sense organs of Scali bregma occur iu each 

 cliEetigerous segment throughout the whole length of the 

 body, midway between the notopodium and neuropodium 

 (fig. 1, S. 0.). The sense organs on the first and second 

 chfetigerous segments are small rounded eminences, very 

 difficult to distinguish in surface view, even with a moderate 

 magnification. Those of the succeeding segments are, in 

 preserved specimens, generally sunk and hidden in a depres- 

 sion bordered by prominent lips of epidermis (tigs. 4, 5). 

 The essential portion of the organ is liable to be overlooked, 

 and the depression, by reason of its prominent lips, may then 

 be readily mistaken for an aperture. The sense organ itself 

 is a papilla arising from the bottom of the above-named 

 depression, its free, oval, curved surface bearing a very 

 narrow, dark, almost flat area, running dorso-ventrally. The 

 sense hairs arise from this darker area or "hair Held" 

 (Eisig), which, in the largest organs of a specimen 56 mm. 

 loug, is only about 50 /i long and 10 — 15^ broad. In this 

 specimen the surface of the free pole of the largest papillae 

 is about 250 fx long aud 90 fi broad. 



The sense organs are best developed in the region of the 

 body just behind the gills. In the posterior third of the 

 animal they gradually decrease in size, and in the last five or 

 six segments they are difficult to find even in sections. 

 About the sixth or eighth segment from the posterior end the 

 organ is recognisable as a minute oval elevation, measuring 

 about 15 fj. along its longer diameter (hg. 7). 



The structure of these organs can be best studied in thin 

 transverse sections of specimens about 15 mm. long (figs. 28, 

 29). The organs have attained almost the same stage of 

 growth even in specimens only 5 — 7 mm. long. 



