21 
of an animal being preserved. The Lias itself has yielded from 
many localities evidences of the skin in Ichthyosaurs, and the 
beautiful example of a Wurtemburg Ichthyosaur, figured by 
Dr Eberhard Fraas, demonstrates that the skin need not follow 
the contours of the bones, since the high dorsal and caudal fins 
are preserved. All that appears to be required for the 
preservation of such soft parts is the absence of bacteria, by 
which decomposition is brought about; and it may be a 
reasonable inference that there is a greater probability of 
an embryo being free from the influence of agencies which 
cause decomposition than most vertebrate structures. 
In this specimen decomposition appears however to have taken 
place after a time. After the external form may have been 
moulded, the internal tissue appears to have been replaced by 
iron pyrites; for vertical sections of the neck of one of these 
supposed foetal plesiosaurs have been prepared from one of the 
fragmentary specimens, without giving any evidence of internal 
structui e beyond a small central canal. After carefully comparing 
these slices with corresponding sections from the neck of embryos 
of reptiles, which Adam Sedgwick, Esq., F.R.S., has had the 
kindness to have prepared at my request, in his laboratory in 
the University of Cambridge, I am unable to affirm that even 
the central canal in the fossil is manifestly identical with any 
structure in existing animals. The longitudinal section of the 
neck, when seen under the microscope, is equally devoid of 
evidence of segmentation, such as might have been expected, 
though the longitudinal canal shows a uniform width, and 
presumably has some relation, if not to original structures, at 
least to mineralization. This evidence of internal structure, 
having failed, I have not thought it necessary to slice up the 
specimen in the way originally contemplated. 
The evidence for the organic origin of the specimens is 
essentially that contributed by their external forms; but not 
one example is sufficiently perfect to show all the details. 
Each of the four principal specimens is characterized by a 
median longitudinal ridge or blunt angle which extends down 
the neck, body, and tail, upon what I regard as the dorsal 
surface ; corresponding in position to the neural spines of the 
vertebrae. In the example numbered 1, in which the head is 
