II. 



Can the Sexes in Ammonites be 

 Distinraished ? 



ALL living Cephalopoda known to us have the sexes separate ; no 

 hermaphrodite species has been discovered. It is therefore 

 natural to suppose that the extinct Ammonites were similarly uni- 

 sexual, some specimens being male, others female. If this be 

 admitted, it becomes of some importance to ascertain whether the 

 difference of sex affected the hard as well as the soft parts of the 

 animal, and, conversely, whether certain differences of form that 

 distinguish individuals may not be of sexual rather than of 

 varietal or specific nature. Clearly it would be wrong to give 

 separate specific names to individuals whose only difference was 

 that of sex. 



The opinion that such secondary sexual characters are manifested 

 in Ammonite shells has long been maintained by many eminent 

 authorities, notably among French palaeontologists. The first to 

 suggest it seems to have been Ducrotay de Blainville, in his 

 "Prodrome d'une monographie d'Ammonites," Paris, 1840. "Un- 

 known," he said, "though the Ammonite animal be, yet analogy drawn 

 from what we know of the Nautilus does not allow us to doubt that 

 the sexes were separate in different individuals. The females, then, 

 must have had the ventral side more swollen by the ovaries replete 

 with eggs at a certain period. Hence the shell and its aperture 

 must have betrayed these differences by a size and swelling in the former 

 and a relative width in the latter, both greater in female individuals 

 than in those of the male sex, since the semen of the males 

 could never reach such a development as the fertilised ova of the 

 females." De Blainville was followed by d'Orbigny and many other 

 palaeontologists. Pierre Reynes, in the Monograph cut short by his 

 untimely death (1879), strongly upholds the distinction of the sexes, 

 saying — " The difference in the dimensions of shells equally orna- 

 mented seems to be one of the most convincing proofs. Among 

 individuals, some are slight and of compressed shape, while the 

 whorls of others are broad ; we think that the first are the males and 

 the second the females. ... It results from the comparison of a 

 certain number of individuals of the same species that, without any 



