574 CEPHALOCHOBDA. 



Amphioxus as that of the pronephric duct in the Craniata, while the 

 genital vesicle of A mphioxus is homologous with the gononephrotomes 

 of the Craniata and consequently also of the canals of the primitive 

 kidney in the latter. Even if we adopt Boveei's homologies, we 

 must still recognise certain distinctions between the development of 

 the urogenital system of Amphioxus and that of the Vertebrata, 

 which, however, would not then be of a fundamental character. 

 Through the great development of the atrial cavity which, according 

 to Boveei, is represented in the Craniata by the pronephric canals, 

 Amphioxus is linked on to the Tunicates. Among the further 

 peculiarities of Amphioxus, we must reckon the development of the 

 so-called anterior entoderm-vesicle and the club-shaped gland, organs 

 as to the morphological significance of which we are at the present 

 time unable to state anything with certainty. 



The peculiarities just mentioned seem to indicate that Amphioxus, 

 as contrasted with the Craniata or Vertebrata, shows, in the strict 

 sense of the term, a certain independence in its position. It would 

 be difficult to find an explanation for this if Ave were to adopt the 

 assumptions of Dohen (p. 522), that Amphioxus is a degenerate form 

 derived from the Craniata. We do not deny that Amphioxus, in 

 consequence of its half-sedentary manner of life (burying in the sand) 

 may have undergone a certain degree of simplification and degenera- 

 tion. Above all, we might in this way explain the slight development 

 of the brain and the sensory organs and also the locomotory system. 

 It is naturally difficult to determine how far the simple structure of 

 Amphioxus rests upon primary peculiarities or to what extent upon 

 peculiarities secondarily acquired through degeneration. The majority 

 of the facts known to us as to the ontogeny and the anatomy of 

 Amphioxus seem to indicate that we have in this case actually to do 

 with a very primitive form. 



Among the peculiarities which we regard as secondarily acquired 

 is the remarkable asymmetry in the structure of the body which is 

 specially marked in the larval forms, but is also retained to some 

 extent in the adult (position of the olfactory pit, of the anus, and of 

 the hepatic caecum, conditions of the innervation of the velum and 

 the definitive mouth according to van Wijhe). Willey's observation 

 that the Amphioxus larva lies when at rest at the bottom of the sea 

 on the right side of the body seems to indicate that this asymmetry 

 is acquired in the same way as in the PleuronecMdae* 



* [According to Wiixey, our authors have misunderstood his observations on 

 this point. The fact that the young when kept in a glass jar sink to the 



