The finer Anatomy of the Nervous System of Myxine glntinosa. 371 



as figured in Edinger (7) we find a somewhat similar arrangement 

 of tlie aqueduct and »Canalis ventriculi terti«, the »Canalis connec- 

 tens« is, however, absent, as is the case in many individuals of 

 Myxine. Taking a sagittal section of a still younger embryo of Tor- 

 pedo, as for instance, one of 30 mm as figured by Edinger (7) it is 

 easy to see that allowing the communication between the infundibular 

 region and the »Recessus praeopticus« to remain during the solidifi- 

 cation of the brain we get a figure very similar to that I have found 

 in Myxine. 



The entire absence of a Cerebellum may be exi»lained by a 

 fact that is pointed out by Edinger (8) and others, that the size 

 of the Cerebellum is dependant on the swimming prower of the 

 different species. Myxine is probably developed from ancestral 

 forms that never have had more than crawling power and it has 

 since remote geological periods existed under similar conditions to 

 those of the present day, viz., creeping about the bottom of the sea 

 in the mud, living on refuse of dead bodies of fishes, etc. This 

 movement may be performed entirely automatically and any organ 

 regulating coordinate movements would be unnecessary. In the dor- 

 sal aspect four double divisions of the brain are seen. The brain 

 is divided longitudinally in two lateral parts by a fissure, each part 

 divided transversely in four lobes by three pairs of fissures. The 

 first pair of fissures runs in a somewhat rostral direction; the second pair 

 laterally and caudally and the third again in a somewhat rostral direction. 



G. Retzius (38) considers the first division homologous to the 

 > Riechhirn« or Lobus olfactorius as already found by A. Retzius (36) 

 and J. Müller (27); the second division homologous with »Vorder- 

 hirn«. The third should be the »Mittelhirn« or Mesencephalon. He 

 finds it more difficult to identify the fourth division, but, like J. 

 Müller, considers it probable that it should be homologous with 

 the »Hinterhirn« or Cerebellum, only he finds it peculiar that it is 

 so highly developed in Myxine when it is so little developed in 

 Petromyzou and considers it impossible to definitely solve the question 

 without the aid of the development., Sanders (11) found that the 

 brain shows very slight indications of divisions into parts. He 

 recognises rostrally the olfactory lobes, separated by a shallow 

 transverse furrow from the Cerebrum behind. Longitudinally the 

 Cerebrum passes without division into a pair of tuberosities behind, 

 which should be in a corresponding position to the Tubereula inter- 

 media of GoTTSCHE. He finds situated between these two lobes a 



