66 
J. BEARD. 
insist against Spencer and Beraneck that de Graaf (No. 8) was 
right in his assertions. 
In PI. II, fig. 13, I have given a figure of the eye in longi- 
tudinal section ; it is taken from an advanced embryo of Anguis, 
and shows very distinctly that the lens is well marked off from 
the retina by a sharp line of division. I could, if I chose, give 
similar sections through adult specimens, showing the same 
fact. 
I should not refer to this apparently trifling circumstance 
were it not of great importance for some considerations to be 
developed further on. 
Regarding Spencer’s speculations on the origin of the 
parietal eye from the larval Tunicate eye, I think I need say 
little more thau I have already said in my paper in 'Nature’ 
(No. 3, p. 246). It reads: "With Wiedersheim and Car- 
riere I consider that Spencer has placed the eye of the larval 
Tunicate at the wrong end of the series — if it should come 
in at all; for, as experience has abundantly shown, it is very 
easy to compare organs of the higher Vertebrates with what 
are supposed to be homologous organs in Amphioxus and the 
Tunicata, and at the same time to be entirely in error. I need 
hardly refer the reader to the instances in which such com- 
parisons have been shown by Dohrn, in his well-known 
‘ Studien/ to have been entirely wrong.” One might suppose 
the degenerate nature of the Tunicata had been sufficiently 
proved, and it is impossible to look with any favour on Spencer’s 
attempt to re-establish that group in the position of ancestors 
of Vertebrates, or, what is practically the same thing, near 
allies of such ancestors. One thing more : in Spencer’s dia- 
grammatic plate (No. 14, PI. XX), illustrating "the rise and 
fall” of the parietal eye, he begins with a slight evagination of 
the brain (larval Tunicate, fig. 1), which shows one layer of 
cells, whose inner ends, their bases, are evenly pigmented. The 
next two stages (PI. XX, figs, ii and in, Bufo) the pigment is 
more confined to the centrally situated cells of the evagination, 
that is, in those cells which, if the thing developed into a parietal 
eye like that of Hatteria, would form the lens. This would 
