xxii Journal of Comparative Neurology. 



investigated in the frog. Burckhardt has for the first time observed 

 and figured it in Protopterus. The saccus communicated by a nar- 

 row neck with the saccukis and utriculus of the auditory vesicle, and 

 with its diverticula overlaid the region of the 4th ventricle, and ex- 

 tended as far back as the ist pair of spinal nerves. 



The memoir contains a short chapter on the phyletic development 

 of the brain of Protopterus. Starting with Selachia, he considers 

 that one line of development has been through Protopterus to 

 Ichthyophis, and thence to the Urodela and Anura ; another through 

 Ceratodus to Reptilia and Mammalia ; whilst a third line is from the 

 Selachia to the Ganoids and Bony Fishes. 



The Structure of Nerve Cells.^ 



Dogiel has investigaied the minute structure of the retina by 

 means of the methyl blue process [precipitating the blue by picrate of 

 ammonia osmic acid mixture) and sums up his results as follows: 



1. The retina contains the following nervous elements: (a) cells 

 with protoplasmic processes and an isolated axis-cylinder process 

 which passes directly into the axis cylinder of a nerve (cells of the first 

 group ;) (b) cells with protoplasm process and an axis cylinder pro- 

 cess but the latter not directly connected with nerve fibres but divid- 

 ing into these branches forming a reticulum; (c) cells with only pro- 

 toplasm processes. 



2. The axis cylinder of nerve fibres begin : (a) directly from the. 

 cell body or a protoplasmic process of such a cell; (b) from the nerve 

 net formed by the axis cylinder processes of the second group, and 

 finally, (c) directly from nervous branches and threads derived from 

 the subdivision of the group III. 



3. The protoplasmic processes of all nerve cells of the retina 

 unite to form a reticulum as a result of which the cells belonging to a 

 group or type are united into a colony. 



4. Like the axis cylinder processes the protoplasmic processes 

 have an indubitable nervous nature and are not related with either 

 the blood vessels or glia cells. 



5. The body as well as the fibres of the nerve cells consists of a 

 fibrous and interfibrillary substance and part of the fibres of a cell pass 

 into its axis cylinder. 



'A. S. Dogiel. Zur Frage iiber den Bau der Nervenzellen und iiber das 

 Verhaltniss ihres Axencylinder-Fortsatzes zu den Protoplasma-fortsatzen. Ar- 

 chiv filr Mikroskopische Anatomie XLI, i. 



I 



