122 THE ANCESTRY OF VERTEBRATES 



(I.e. p. 599) the "collar-cavities" of Amphioxus and thus 

 homologized to the homonymous cavities of Balanoglossus. 

 The other mesodermic segments, according to him, are 

 all separated from in front backwards from a pair of 

 "coelomic grooves" which after their separation from the 

 entoderm communicate with the gut only at their posterior 

 ehd. They are compared with the trunk coelom of 

 Balanoglossus. 



Van Wyhe (1902, p. 176) joins Macbride in his deri- 

 vation of the metamerism of Amphioxus from an original 

 trimerism as in Balanoglossus and tchinoderm-larvae and 

 tries to extend the comparison also to Craniates. Protocoel, 

 mesocoel and metacoel, proto-, meso- and metasoma accord- 

 ing to this conception may be distinguished in Chordates 

 as well as in Balanoglossus and other deuterostomian 

 "Prochordates". The opening of Hatschek's pit is compared 

 by Bateson (1885) with the proboscis-pore of ^fl/aAZ(?^/6»ss«s 

 and the water-pore of Echinoderms. GOODRICH (1917) tries 

 to extend this comparison to the so-called premandibular 

 somites of Craniata. He claims that in Selachii these acquire 

 an opening into the hypophysis which he homologizes with 

 the preoral pit of Amphioxus, In this direction then the 

 connection of the Chordates with Evertebrates has been 

 sought in recent times. 



From the point of view of my theory, however, these 

 recent attempts to solve the old question cannot lead to 

 any good. In my opinion the metamerism of Vertebrates 

 has been directly inherited from the Annelids and has nothing 

 to do with the trimerism of the so-called "Hemi- and Diplo- 

 chordates" of BATESON and MASTERMAN. Truly, in the 

 Annelid body also, we can, if we wish, distinguish three 

 regions, the prostomium, the peristomium and the rest of 

 the segmented body. The situation of the mouth agrees with 

 that of Balanoglossus in that it lies in front of the peristomium 

 and the collar respectively. Whether a deeper significance is 

 to be attributed to this agreement (cf. SPENGEL, 1893) is 

 a question as obscure as that of the relation of Proto- and 

 Deuterostomia to one another. Probably, however, they have 

 nothing to do with each other. 



Brain vesicle of Amphioxus — Another question raised by 

 .the comparison of the anterior end of the body in Acrania 

 and Craniata is that of the relation of the brain vesicle of 

 the former to the brain of the latter. Several attempts have 



