278 



PKOCEEDINGS OF THE M/HACOLOGICAL SOCIETY. 



Tlie evidence adduced, in a memoir {I4.2) that all should read, may 

 be summarized as follows: — In the JN'autilus shell the dorsal or inner 

 side of each whorl is channelled and into this groove ('contact 

 furrow ') the preceding whorl fits. Now in the early nautiloids the 

 young shells, which are not closely coiled, show no sign whatever 

 of such furrow, but with the growth of the shell, and the increased 

 tendency to closer coiling, this groove develops as the succeedino- 



I. II. 



Diagrammatic Sections of Nautiloid Shells. 

 I. Of an early type, in which the initial whorls (A, B, C), not being in contact, 

 show a sectional outline devoid of indentation, while the later ones (D, E, F) 

 show a ' contact furrow.' 

 II. Of a late type, in which the initial whorls (A, B, C), still not in contact, 

 exhibit an 'impressed zone,' the precursor of the 'contact furrow' in the 

 later ones (D, E, F). 



whorls come in contact, and it not only becomes more and more 

 pronounced in the different forms which follow on in time, but tends 

 by the law of acceleration to develop earlier and earlier in the life- 

 history of the individual, till it is shown, as in the modern Nautilus, 

 as an ' impressed zone ' in the verj^ earliest stages, before a single 

 complete whorl has been formed, when its existence serves no purpose, 

 and it simply . foreshadows a need to come. Hyatt regards the 



