ENTEROPNEUSTA 



389 



lo not allow ns to put any great weight on such an in- 

 jrpretation of the acorn. A comparison of the Tornaria 

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

 jiliated bands so characteristic of the latter present here 

 [uite a different distribution. Moreover, the 'Tornaria ap- 

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

 bhe Echinoderm larvae. The latter likewise exhibit no 



[eye-spots. The resemblance between the Tornaria and the 



[Echinoderm larvae is therefore of a rather superficial nature, 

 'he possession of an apical plate and the cords radiating 

 Prom it point rather to relationships of the Tornaria with 

 the Trochophore. 



The occurrence in Balanoglossus of paired coeloraic sacs, 

 lying one behind the other, indicates a segmentation. In 

 t;his, it is true, a resemblance to the Echinodermata would 

 jxist, if the statement should be confirmed that in the 



[latter also several pairs of ccelomic 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 

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

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

 [has been especially in mind, and the comparison 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 

 3oelomic 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 

 [ccelomic sac in Balanoglossus. 



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

 'between Enteropneiista 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, comparable 

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

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

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



