260 



modaeum, Balfour) in sich, das sich in das innere Schnabelskelet 

 und den Reusen-Apparat differenzirt. Merkwürdigerweise ist er 

 aus drei gleichen Theilen, Antiineren, zusammengesetzt, deren 

 einer oben, die beiden andern seitlich unten gelagert sind". 



This opinion is shared by Meinert who goes a little farther. 

 For, while according to Dohrn's idea, the organ has no homo- 

 logy among the Arthropoda, Meinert finds this very aualogy 

 everywhere amongst the Araehnida, to which, according to 

 the writer, the Pycnogonida are related. The following quo- 

 tation renders bis view: »I suppose that the proboscis of the 

 Pycnogonida will be found throughout the class of Araehnida, the 

 only difference being that here it is free, large and predominant, 

 while in the other Araehnida it most frequently is very small and 

 hidden betweeu the gnathites" '). The organ is then compared 

 with a similarly formed proboscis in the reuiarkable genus Koe- 

 nenia, and reference made to the mouth-parts of mites, of leeches 

 and of Tipulidae, where we also find three parts as a basis. Accor- 

 ding to him, the presence of these three antimeres is accounted 

 for by simple mechanical laws. 



In the following pages I shall try to show that this combi- 

 nation of three parts of the proboscis can really be explained by 

 the aid of such simple mechanical laws; that they are not exclu- 

 sively found in the Pycnogonida; and that, therefore, Dohrn's 

 theory (eine Bildung sui generis) is not quite correct. 



If we imagine a sucking-apparatus in its simplest form, for 

 instance a tube, we shall find that inside the walls of this cy- 

 linder the muscles effectiug contraction and expansion of these 

 walls, will have to be present in the shape öf circular and radial 

 muscles. If the organ has, moreover, flabby walls, longitudinal 

 muscles are required. The pharynx of many animals is constructed 

 like this, and effects expansion, contraction and shortening. I may 

 mention the presence of this organ in Turbellarians, Trematodes 

 and Nemertines. 



1) Meinert, The danish ingolf-Expedition. Pycuogonida, 1899, p. 19. 



