264 



come to the conclusion that the nurnber of three is not abso- 

 lutely indispeusable in the construction of this proboscis; that it 

 has developed in consequence of inechanical influences and that 

 two antimeres are sufficiënt for suction. 



All we know about the development of the organ supports the 

 opinion defended in the foregoing pages. Not only not a tracé is 

 to be seen of mandibles or other mouth-pieces growing together, 

 but the very earliest form of the proboscis already is cylindrical 

 with immoveable chitinised walls. No wonder, therefore, that, as the 

 larvae immediately after hatching use it as a putnping-apparatus, 

 the only construction possible is that claimed for by mechanics. 



In connection with this I raay describe another case, where the 

 proboscis, indeed, partly retained its triplicity, but iu other respects 

 shows material changes. We found this organ in a new deep-sea 

 genus ') brought home by the Siboga-Expedition. It is (fig. 7) 

 elongate and thin and shows a proximal swelling in which the so- 

 called »Reuse" (Dohrn) is found. In this thicker part the construction 

 of three antimeres and the muscle-fibres can be distinctly seen. The 

 remaining two thirds, form a tube, about 0.04 mm. in width, the 

 muscles of which cannot be traced at all. At the extremity the 

 three lips are entirely grown together, so much so that only an 

 aperture of about 0.007 mm. is left for the absorption of liquids. 



Resuming, we find here a deviation from the general type. The 

 greater part of the proboscis is exceediugly thin, without muscles, 

 only the basal part effects the suctorial movements. The rudimentary 

 condition and the fusion of the lips is bound up with this. 



PIPETTA ïiov. gen. 



Body slender, manifestly articulated ; lateral processes long, 

 separated by large intervals; proboscis bottle-shaped, very long 

 and thin ; abdomen also long and thin. 



Chelifori wanting. 



Palpi slender, longer than proboscis, 8-jointed. 



1) Pipetta, see below p. 265. 



