Oll the coniiei'iive tissue» and body cavities of the Ncmerlenns. 37 



tive, approximatiug closely to the embryonal iiieseiichym , and is 

 probably the parent form of the other tissues. Thus, l)y the pro- 

 duction of a more or less dense, intercellular substance, the connective 

 tissue elements with such an intercellular substance Avould be formed. 

 Another line of ascent from the mesenchym tissue, wliereby no inter- 

 cellular substance is produced, but by a greater ditlerentiation of the 

 cell fibres, and by the cell abandoning its more primitive bipolarity 

 and becoming multipolar, would lead to the interstitial tissue of the 

 body epithelium, the intracapsular tissue of the nervous system, and 

 the pigmented tissue of the body wall (this latter only in Lineus). 

 These relationships of the various Nemertean connective tissues may 

 be illustrated graphically as follows : 



I. P a r e u c h y m. II. M e s e n c h y m. 



1. Intracapsular connect. <_«— — y' \. Connect, tissue with 



tissue y/^ \. intercellular substance 



2. Interstitial tissue of " 3. Pigment, tissue of 



body epithelium body wall {Lineus) 



B. Notes on Classification. 



Bükger (95 a, b) has united my ('95 a) genus Stichostemma with 

 the genus Tetrastemma, saying ('95 a): "Auch der Aufstellung einer 

 neuen Gattung für die Berliner Süsswassernemertine kann ich vorläufig 

 nicht beistimmen, da sich St. eilhardi von den marinen Tetrastemmen, 

 z. B. T. flavidum, doch nur durch seine Zwittrigkeit und seine grössere 

 Augenzahl unterscheidet". But had this investigator read my paper 

 more carefully, he would have noted that Stkliostemma differs from 

 Tetrastemma also, in that its rhynchocoel does not extend to the 

 posterior end of the body, as is shown in my ('95 a) fig. 17, and that 

 it has only 9 longitudinal nerves in the proboscis. The separation 

 of the two genera, on the ground of the difference in the number of 

 the eyes, of the sexual phenomena, of the proboscis nerves, and dif- 

 ference in the length of the rhynchocoel, is certainly based on more 

 important structural differences, than is Burger's ('951)) separation 

 of Oerstedia from Tetrastemma, on the morphologically unimportant 

 ground, that the former is stitfer, and more cylindrical in shape. I 

 have also, recently, found another distinctive character for Sticho- 



