CAMBRIAN ROCKS AT DOSTHILL. 
261 
strange to say, is placed on the inner surface inside the brain. 
From this fact Professor Lankester argues that the ancestral 
form must have been a transparent animal and have had an 
eye ora pair of eyes inside the brain. To explain the presence 
of the two lateral eyes in the Vertebrates we could suppose 
either that the single eye of the Ascidian was shifted to one 
side, and a second developed on the other; or that the 
ancestral Chordate had two lateral eyes, one of which the 
Ascidian larva has lost; or that two lateral eyes have been 
developed independently of the median which has disappeared. 
The latter theory is doubtless correct, as the median eye of 
Hatteria is evidently homologous with the single eye of the 
Ascidian. Probably the arrangement of the retinal layers 
according to the invertebrate type is due to the direction of 
the eye in Hatteria being altered, as it looks away from the 
brain instead of into its cavity. But a study of its develop¬ 
ment in various animals will no doubt explain this difficulty. 
The discovery, then, of this median eye in Hatteria con¬ 
firms the theory that the Ascidians are closely connected with 
the Vertebrates, and adds another detail to the idea previously 
formed of the ancestor of the Chordata—that it had a single 
median eye. 
In conclusion I would remind all readers of this paper 
that our knowledge of this and kindred subjects will be 
materially increased by the investigations of the Marine 
Biological Association, and would suggest that subscriptions 
to its funds will speedily result in definite acquisitions to that 
knowledge. From this and other sources we may hope to 
glean such information that ere long we shall be able clearly 
to trace that most interesting of pedigrees, the descent of 
Man. 
ON THE DISCOVERY OF ROCKS OF CAMBRIAN 
AGE AT DOSTHILL, IN WARWICKSHIRE. 
BY W. JEROME HARRISON, F.G.S. 
The Geological Survey Map of the Warwickshire Coalfield 
was executed between 1851 and 1854. It shows Dosthill as a 
mass of greenstone—bounded on the west by a line of fault 
which is also the boundary of the coalfield—and on the east 
breaking through, tilting, and burning the coal seams of the 
district. 
The real structure of the little Dosthill ridge is rather 
different. When I made my first visit, on May 29tli, 1882, 
