RELATION OF THE NEMERTEA TO THE VERTEBRATA. 643 



brata), we might now consider whether any remnants of the 

 median dorsal cord are retained in those descendants in which 

 the lateral cords have diflferentiated into brain-lobes, oesopha- 

 geal ring, and ventral cord (the Annelida) . To this question 

 1 have no definite answer to oflfer, but I may call attention to 

 the significant fact that the beautiful and exemplary investiga- 

 tions into the embryonic development of Lopadorhynchus, 

 very recently published by Kleinenberg/ have demonstrated 

 the existence in the larva of that Annelid of a nerve-stem 

 answering to the conditions here required. It is dorso-medially 

 situated, it is anteriorly connected with the brain, or rather 

 with a transverse nerve-tract (Kleinenberg's prototrochal nerve- 

 ring), which in its turn is connected with the brain,^ it appears to 

 be connected close to the anus with the ventral cord (the fused 

 lateral stems), and though appearing in early larval life, and 

 having only a temporary existence, it is regarded by Kleinenberg 

 as having considerable physiological importance. If the light 

 in which I am inclined to look at it is not deceptive, its 

 morphological significance also can hardly be overrated. 



In closing this chapter of general considerations we may 

 ouce more bring before our minds the proposition with which 

 it was opened. We have here and in the foregoing chapters 

 adduced facts and arguments which appear to speak in its 

 favour ; we will once more rapidly enumerate the common 

 characteristics of Nemertea and Coelenterata, as well as those 

 of Nemertea and Chordata. 



The Coelenterate characteristics that are also found in the 

 Nemertea are the following : 



a. The presence of nematocysts in the proboscidian 

 epithelium. 



b. The elaborate nerve-plexus in the integument, and its 

 histological features. 



c. The presence of epiblastic muscle- fibres separate from the 

 general body-musculature. 



1 ' Zeitschr. f. wiss. Zool,,' Bd. xliv, Heft, i, ii, October, 1886, p. 107; 

 pi. vii, fig. 27«. 



^ Eor comparison with the Nemertea, cf. PI. XLII, fig. 1. 



