296 GENERAL SUMMARY TO 



by Carpenter and King. The number of caeca on the same part of the shell-surface in 

 very old and very young specimens of Waldheimia cranium was found to be the same. 

 This fact shows that the distance between two caeca does not change with age, and led 

 the author to the conclusion that no intussusception occurs during the growth of the shell. 

 The bases of the calcareous prisms were found to be very regularly shaped at the margin 

 of the shell, but (especially in Terebratula and Terebratulina septentrionalis) they became 

 very irregular towards the older parts. The concentric lines of growth occurring on the 

 outer surface were totally absent on the inner surface, which is explained by supposing 

 the apposition at the margin to stop for some time ; the formation of new layers 

 at the whole under surface at the same time continuing. The chief result of the investi- 

 gation of the body-wall (with its pallial lobes) on surface-views and sections was the 

 demonstration of the non-existence of the lacunary system described by Hancock. Under 

 the simple epiblastic epithelial layer was found a homogeneous intercellular substance, 

 containing a reticular network of multipolar cells, a ' mesenchymatic ' layer. These 

 cells had probably been mistaken by Hancock for a system of lacunary spaces. At the 

 side of the ccelomic cavity the body-wall shows a layer of flat epithelial cells." 



I must, however, remark that Hancock's lacunae have been seen by Mr. Dall in some 

 species, while in others they are invisible and apparently absent ; and he adds that this 

 is even true in some individuals of a single species. 



Having briefly alluded to the exterior of the shell, as well as to its structure, it will 

 be now necessary to notice its interior surface ; but to this subject we shall have to refer 

 more fully in the sequel. 



Mr. P. H. Carpenter remarked when receiving the Lyell Fund (' Q. J. Geol. Soc,' 

 vol. xxxix, Proa, p. 35) — " I have the strongest conviction (and many mistakes would be 

 avoided were it a universal one) that the only way to understand fossils properly is to gain a 

 thorough knowledge of the morphology of their living representatives. These, on the other 

 hand, seem to me incompletely known if no account be taken of the life-forms which have 

 preceded them." This has been constantly the view I have taken and followed since the 

 time I first began my studies in connection with the Brachiopoda ; and I have never lost 

 an opportunity in making myself acquainted with the living forms and their animal, as 

 well as in urging similar investigations to be undertaken by eminent zoologists and ana- 

 tomists, who were more competent than myself to advance our knowledge in that 

 important subject. How can we understand those varied and complicated processes and 

 impressions seen on the interior surface of the fossil shells of extinct species, if we do not 

 make ourselves acquainted with them and their functions in the living forms ? Once 

 acquainted with these, it becomes a comparatively easy matter to interpret them and their 

 functions in their fossil representatives. I have always maintained that the study of the 

 interior characters are of paramount importance in the discrimination or classification of 

 genera and families. 



Eor the present I shall content myself by observing that on the inner surface of 



