505 



in its anterior portion. There is a posterior portion of the ventricle in- 

 timately associated with a ganglionic tract which corresponds with the 

 mesocoele; while the myelocoele remains more or less widened, vary- 

 ing much in thickness in different individuals ; but always in an un- 

 differentiated state. 



2) The large collections of ganglion cells just posterior to the 

 thalamocoele are homologous with the medullary nuclei of other verte- 

 brates, since their connections show them to be centres for the con- 

 trol of the branchial apparatus and the sensory and motor structures 

 lying in the territory of the gill basket, — e.g. centre of respiration, 

 deglutition, etc, 



3) The ontogenetic changes of the neural axis in other vertebrates 

 carries the brain through the condition which in AmpMoxus remains 

 permanent as the adult brain. 



4) All the sense organs developed in connection with the anterior 

 end of the Amphioxus body are probably paired, some of them cer- 

 tainly are, e. g. the eye-spot. 



5) The eye-spot or eye of AmpJiioxus is the forerunner of the ver- 

 tebrate eye and shows traces of several stages in the development of 

 the retina of higher forms. In itself it is not an organ of sight, but a 

 light perceiving organ. 



6) The pigment of the eye spot oî Amphioxus is contained in cells 

 which always lie inside the bounds of the nerve mass, and whenever 

 outside in preparations is to be considered as misplaced by chemical 

 or mechanical means. 



7) The pigment bodies of the central nervous system oi Amphioxus 

 are connected with and form a part of segmental sensory structures. 



8) Each one of the pigment bodies is connected with (forms a de- 

 posit in) an amoeboid cell. All these cells retain their amoeboid nature 

 throughout life, the pigment cells of the eye spot not excluded. 



9) The pigment of the axial nervous system of Amphioxus is in 

 process of migration towards the anterior end of the body — towards 

 the eye. 



10) The conclusion that the giant ganglion cells of the anterior 

 portion of the spinal cord of Amphioxus send out axis cylinders only 

 caudad (Rhode) is erroneus, and as my preparations show S ti e da's 

 observations are correct both in figure and text. 



11) The lack of development of the organs of excretion in Am- 

 phioxus may be due to the extremely slight metabolism of the body, 

 consequent on its mode of life, Avhich is known to involve a minimum 

 of muscular activity, while its muscles form more than 500/o of the 

 metabolic tissues of the body. 



