ENTEROPNEUSTA 389 



do not allow us to put any great weight on such an in- 

 terpretation of the acorn. A comparison of the Tornaria 

 with the Echinoderm larva is difficult to carry out, for the 

 ciliated bands so characteristic of the latter present here 

 quite a different distribution. Moreover, the Tornaria ap- 

 pears to possess a kind of apical plate, which is absent in 

 the Echinoderm larvas. The latter likewise exhibit no 

 eye-spots. The resemblance between the Tornaria and the 

 Echinoderm larvee is therefore of a rather superficial nature. 

 The possession of an apical plate and the cords radiating 

 from it point rather to relationships of the Tornaria with 

 the Trochophore. 



The occurrence in Balanoglossus of paired coelomic sacs, 

 lying one behind the other, indicates a segmentation. In 

 this, it is true, a resemblance to the Echinodermata would 

 exist, if the statement should be confirmed that in the 

 latter also sevei-al pairs of ccBlomic sacs are developed 

 (comp. p. 414). This internal segmentation of the larva 

 subsequently disappears, and the segmentation which can 

 be recognized on the adult Balanoglossus has nothing to 

 do with it. 



In searching through the animal kingdom after relationships for 

 Balanoglossus, characterized as it pre-eminently is by the possession 

 of gills, a comparison with the Chordata has been reached ; but there is 

 as yet no adequate basis for this comparison. It is Amphioxus which 

 has been especially in mind, and the comijarison has been based chiefly 

 on the gills, on the intestinal diverticulum, called by authors the 

 chorda, and its skeletal body, and on the formation of the nervous 

 system. A striking resemblance is noticeable between the anterior 

 ccelomic sacs of Balanoglossus and the most anterior archenteric diver- 

 ticula of Amphioxus, which also make their appearance very early, and 

 one of which greatly enlarges and opens to the exterior by means of 

 a ciliated canal, like the so-called water-vascular vesicle or the anterior 

 coelomic sac in Balanoglossus. 



[To what precedes we append the following : The supposed relations 

 between Enteropneusta and Chordata have become, according to recent 

 observations at least, very doubtful. The diverticulum of the intestine 

 in the acorn, or rather the acorn skeleton, is, as it appears, comjjarable 

 with the chorda neither in regard to its origin nor structure. The needed 

 agreement in the formation of the nervous system seems, in fact, to be 

 wanting. The gills of Balanoglossus, it is true, are strikingly similar 



