449 



of Balanogïossus^ and have fused dorsally but without pre-oral exten- 

 sion in the Eu-chorda. Although I naturally attempted to shew that 

 the condition in Balanoglossus could be derived from that in Cephalo- 

 discus by fusion and pre-oral extension, this question is absolutely 

 apart from the derivation from the latter of the euchordate condition 2. 



The homology of the paired 'lateral notochords' in Actinotrocha 

 and those of Cephalodiscus appears to me to be indisputable, for they 

 are identical parts of the same organ, with an identical structure, in 

 two closely allied species. 



Mr. H arm er appears to be in some difficulty about this, through 

 he suggests that the lateral notochords oi Actinotrocha may be homolo- 

 gous with 'the dorsal branchial part of the pharynx of Ceiihalo discus^ 

 almost the whole of which is formed by the lateral notochords of this 

 species. 



In PI. XXVI fig. 21 I figured the lateral notochords oi Actino- 

 trocha and compared them directly with 'the dorsal branchial part of 

 the pharynx of Cephalodiscus' (PI. XXVI fig. 22). Such being the case 

 it can only be supposed that Mr. Harm er thinks, that on the whole, 

 their homology may be accepted. 



As regards the absence of pigment in the notochords of Actino- 

 trocha^ Mr. Harm er considers the evidence insufficient. In PL XXI 

 fig. 30 is represented the appearance, as seen in surface view, of the 

 vesicles. Thereafter, no less than ten sections (figs. 30a — 37) of these 

 vesicles are figured, with not a trace of pigment in any of them. It 

 seems to me that further evidence than this does not come within 

 the usual scope of morphological literature. The most casual inspec- 

 tion of the living larva would convince Mr. H armer, or any other 

 worker familiar with the microscope, of the truth of these statements. 

 Meanwhile I must rely upon other zoologists not to assume that I have 

 drawn the figures alluded to, and deliberately left out all pigment 

 that might have been present. 



In conclusion, it appears to me that those who in the meantime 

 will allow of no Chordate affinities in the Archi-chorda (Entero- 

 p ne usta, Cephcdodiscus and Phoronis) and assume that the gill-slits, 

 mesoblastic skeleton, notochords, and dorsal nervous system in these 

 species are all convergent imitations of the similarly-named structures 

 in the Eu-chorda, will deem Mr. Harmer and myself equally 

 Avrong in our attempted homologies. 



- In this connexion, not only is the notochord in the young Balanoglossus 

 paired at its base, as figured by Morgan (loc. cit. PI. XXVIII fig. 58), but this 

 author figures a chordoid condition of the gill-slits in fig. 65. Compare also Figs 4 

 and 5. 



