368 A. A. W. HUBltECHT. 



of Nemertines arise as part of the coelom (cf. Lang, ' Gunda 

 segmentata ) ? What is the morphological significance of the 

 generative ducts which establish a direct communication be- 

 tween these sacs and the exterior, and which are recognisable 

 on the outer surface as a double set of symmetrical pores ? Is 

 the paired nephridium provided with internal openings or is 

 it not ? These and other questions will have to be diligently 

 studied and solved before comparison can extend itself in the 

 domain of these organs. 



With respect to the vascular system, it is not unimportant 

 that in Nemertines it is on the whole a closed system of vessels, 

 sometimes carrying corpuscles charged with haemoglobin, 

 sometimes colourless, and giving off a system of transverse 

 connecting vessels, which link together the three longitudinal 

 stems. These transverse vessels do not give off any capillaries, 

 and are metamerically placed with unbroken regularity, one 

 for each internal metamere (intestinal diverticulum). If indeed 

 the suggested homology might prove to hold good between these 

 diverticula and the mesoblastic somites of Aniphioxus, the 

 significance of this regular disposition, one for each of the 

 transverse subdivisions of the body, corresponding in a general 

 way to the arrangement of the aortic arches in vertebrate em- 

 bryos could not be overlooked. 



In conclusion I would point out that the speculations and 

 suggestions contained in the last pages ought to be distin- 

 guished from the contents of the first part of this article. 

 They have not in any way contributed to the formulating of 

 the hypothesis there brought forward ; they are merely the 

 sequel in a train of thoughts which, starting from a comparison 

 of such important and primitive organs in both Vertebrates 

 and Nemertines as are the nervous system, the hypophysis 

 and the notochord necessarily extended itself to other struc- 

 tures and organs occurring in both groups. 



With respect to these, we must await more thorough inves- 

 tigations before pushing our speculations further. 



