lOO ANATOMY OF AMPHIOXUS. 



RiJCKERT that these vessels occur in the same segments as the 

 rudimentary pronephric tubules, and give rise to rudimentary 

 glomeruli at the level of the tubules. (Cf. Fig. 35 B.) There 

 can be no doubt that these vessels are homologous with the 

 vessels which run through the primary branchial bars of Aniphi- 

 oxus, and, as shown by Boveri, assist in forming glomeruli at the 

 level of the excretory tubules. 



The morphological importance of these facts is very great and 

 has been strongly emphasised by Boveri. Whether Paul Mayer's 

 connecting vessels indicate the former existence of gill-slits in that 

 region is not so certain, since it is difficult to decide whether 

 the indefinite number of gill-slits in the adult Amphioxus is a 

 palingenetic (ancestral) feature or not. It should also be remem- 

 bered that Paul ]\Iayer found numbers of connecting vessels, 

 between sub-intestinal vein and dorsal aorta, in the tail. 



7. (p. 78.) Boveri found that the epithelium of the pronephric 

 duct of Myxine was of a glandular nature, comparable in this 

 respect to the atrial epithelium of Amphioxus. 



8. (p. 86.) As shown in Fig. 43, Rohde was inclined to 

 follow Schneider in the belief that the fibres of the ventral spinal 

 nerves were directly continuous with the muscle-plates and, more- 

 over, exhibited the same striation as the latter. It has recently 

 been shown by Gustav Retzius that this appearance of continuity 

 is an illusion, as in so many other cases where nerves have been 

 wrongly supposed to enter into direct continuitv with peripheral 

 end-organs. By employing Ehrlich's method of staining nen-ous 

 tissue, intra vitain, with methylene blue, Retzius has proved that 

 the motor fibres of Amphioxus pass with a somewhat winding course 

 between the muscle-plates, and simply end on the surface of the 

 plates. Rarely they branch dichotomously, but there is no special 

 end-apparatus as in the higher forms. Their connexion with the 

 muscle-plates is, therefore, one of intimate contiguitv, but not of 

 continuity. 



9. (p. 91.) The cerebral vesicle of Amphioxus was discovered 

 in 1S58 by Leuck.irt and Pagenstecher. Owsj.-vxnikow (1S6S) 

 thought it represented the fourth ventricle of the vertebrate brain. 

 Stieda (1873) ^^^s '^^ first to homologise the cerebral vesicle of 

 Amphioxus with the entire brain of the higher forms, and to regard 



