56 CHORDA DORSALIS OF ASCIDIAN LARVA ? 



animals destitute of limbs altogether, so there are 

 wingless insects. 



The example of a transition of structure between 

 the invertebrata and vertebrata just adduced is not, 

 perhaps, such as would be recognised by Haeckel, 

 seeing that, in his opinion, arthropods have but a 

 remote phylogenetic relationship with the vertebrata. 

 It is in my opinion more indisputable, however, 

 than the notorious alleged homology between the 

 embryo of the ascidian mollusk and that of the 

 vertebrate amphioxus or lancelet, on which Darwin 

 and Haeckel rely with so much confidence as an 

 example of the. connecting link between the inver- 

 tebrata and vertebrata. 



It is difficult to recognise in the chord-like struc- 

 ture as described by Kowalevsky in the transitory 

 tail of the ascidian larva a homologue of the chorda 

 dorsalis of the vertebrata. If the single ganglion of 

 the ascidian correspond, as is supposed, to the so-called 

 supra-sesophageal ganglion of worms, the side on 

 which this single o-anMion is situated must in that 

 case be really the ventral (as I have shown) ; and 

 consequently the body supposed to be a dorsal chord 

 does not bear the proper relative position which in 

 the vertebrata the chorda dorsalis bears to the spinal 

 cord. In fact, Kowalevsky's cord has not, in my 

 opinion, the significance of a chorda dorsalis at all. 



This disallowance of the alleged close relation- 

 ship in their ontogenesis between the ascidian and 



