ORIGIN AND STRUCTURE OF THE HEAD 55 



to that of Amphioxus than in the former, though there can 

 be no question of h direct homologization ofthelwo. This 

 starting point of KUPFFER has been shown to be a false 

 one, though his conclusion, that the end of the brain-axis 

 of Craniates is found in the neuropore, is not therefore 

 necessarily to be rejected and at any rate seems to me to 

 be preferable to hiss and Hatschek's assumption of 

 a linear fore-end of the brain. No doubt both the latter 

 investigators were right in emphasizing that the part of 

 the brain in front of the infundibulum is a later acquisition, 

 not yet present in the brain of Amphioxus, but their concep- 

 tion of the way in which it has originated needs modification. 



The question of the axis of the brain has lost much of 

 its importance in the light of my theory, which no longer 

 permits a comparison of the fore-brain of the Craniates with 

 the brain-vesicle of Amphioxus in the sense of V. KUPFFER, 

 but, if we want to speak of a brain axis, I think it preferable 

 to let it end in the neuropore which, just as in Amphioxus^ 

 designates the anterior termination of the dorsal suture. 

 This implies, that the lamina terminalis represents the 

 primary floor of the fore-biain, not a part of the original 

 roof with a median suture, as supposed by HIS and others. 



Lateral sense-organs in Annelids. — If our conclusions 

 are hitherto correct, it must be admitted, that hardly two 

 of the great sub-kingdoms or phyla of the animal kingdom 

 show such a close agreement, even in the details of their 

 structure, as Annelids and Vertebrates, and in no other 

 case can the structure of the one be derived so completely 

 from that of the other. This consideration makes it appear 

 not quite so improbable, that ElSIG (1887) was not wrong, 

 when he believed he had found again also the so-called 

 sixth sense-organ of lower Craniates in Annelids. After 

 Parker's (1905) experiments the function of the organs of 

 the lateral sense-line is the perception of water vibrations 

 of low frequency, produced by the waves on the surface 

 and by bodies falling into the water, while HOFER (1909) 

 ascribes to them only the faculty of perceiving the constant 

 pressure of water-currents. With the exception of Capitella, 

 EISIG (1887, p. 501) finds in all Capitellids, nearly along 

 the whole length of the body, in every segment a pair of 

 roundish prominences, situated laterally between the neural 

 and the haemal parapodium near the hinder limit of the 

 segment, it is just on the boundary- line of haemal and 



