VERTEBRATES FROM A CRUSTAOEAN-LIKE ANCESTOR. 397 



the coagulum of the albuminous fluid which the central cavities 

 contain. 



Mr. Hardy kindly undertook to make specimens for the ex- 

 press purpose of solving this question^ and found conclusively 

 that cilia are present in the cells lining the brain-cavities, and 

 also on those of the choroid plexuses. The brain-cavities were 

 opened, and a small portion of the lining epithelium, as well as 

 of the choroid plexuses, examined in normal saline solution in 

 the living condition ; in various places the action of the cilia 

 upon small fatty particles and even red blood-corpuscles was 

 very clearly visible. Other portions were taken, washed out 

 with normal saline solution, and exposed to the action of osmic 

 vapour; sections then showed clearly a fringe of short cilia 

 standing out from the lining epithelial cells. 



So far, in considering the relations between the cephalic 

 stomach and the infra-oesophageal and thoracic ganglia, I have 

 dealt mainly with the changes of the stomach wall in conse- 

 quence of its altered function, and have merely incidentally 

 mentioned that the compression of a ventral fold of the 

 stomach by which the raphe is formed was due to the growth 

 of the nervous masses of the fused infra-oesophageal and 

 thoracic ganglia ; I will now shortly consider the structure of 

 that portion of the brain of the Ammocoetes which I look 

 upon as formed by these ganglia : at the same time I feel 

 that I cannot, as yet, compare the structure of the two nervous 

 systems in such minute detail as I feel convinced further 

 investigation will enable me to do. I desire at present merely 

 to point out that there is nothing in the structure and arrange- 

 ment of the nervous elements in the epichordal portion of the 

 brain which is inconsistent with the supposition that we have 

 here the fused infra-oesophageal and thoracic ganglia of the 

 Crustacean-like ancestor. 



The structure of the Arthropod nervous system may be 

 described as consisting of nervous elements, held together by 

 a framework of supporting tissue, the nervous elements con- 

 sisting of — (1) nerve-fibres which connect the different gan- 

 glia together and form the outgoing nerves ; (2) groups of 



VOL. XXXI, PART III. — NEW SEK. D D 



