154 



ON THE CALCAREOUS EGGS OF TERRESTRIAL 

 MOLLUSCA. 



(Presidential Address delivered at the Annual Meeting, October 14th, 1916). 



By ROBERT STANDEN, 



Assistant-Keeper of the Manchester Museum. 



No class of animals possesses more variety or curious complexity of 

 the reproductive system than the mollusca, and the study of the 

 various methods exhibited in the deposition of their eggs has long 

 been a source of attraction to me. More especially lias this been the 

 case with those species producing eggs with calcareous shells, which 

 admit of ready preservation as an interesting adjunct to a collection, 

 but are largely neglected by amateurs. Some lime ago, on the occa- 

 sion of one of the pleasant re-unions of northern conchologists, held 

 periodically at the Manchester Museum, I exhibited some of my 

 snails' eggs, and gave a short paper upon them. This was so much 

 appreciated, that I have decided to again take up the subject as the 

 theme of my Presidential Address, confining my remarks entirely to 

 the calcareous eggs of certain groups of terrestrial mollusca, in an 

 attempt to roughly summarise the extent of our present knowledge of 

 them, as evidenced by the recorded notes and observations of various 

 conchologists. 



References to the eggs of land shells — whether calcareous or 

 otherwise — are very scanty in the works of the older conchological 

 writers, and then usually limited to a casual mention of eggs of the 

 larger species of jBtilimus, Achatina, or Acavus. Latterly, however, 

 more attention has been given to them by modern authors, so that 

 in the writings of Tryon, Pilsbry, Hedley, E. A. Smith, Suter, and 

 others, we find detailed descriptions, sometimes accompanied by 

 figures, of a number of species. But at present the total number of 

 known kinds of eggs, as compared with the vast array of described 

 species of exotic land shells, is very insignificant. 1 am pleased to 

 see that special attention is being given to the oviposition of our 

 native species by Mr. J. W. Taylor in his " Monograph of British 

 Mollusca." 



The eggs of snails rapidly increase in size after deposition. This is 

 especially noticeable in those with membranous envelopes, but is also 

 observable in the calcareous kinds which rapidly acquire opacity and 

 hardness, through the gradual deposition of innumerable limy par- 

 ticles over the whole inner surface of the egg. These particles attain 

 a maximum development in the Helicidce, and assume the form of 

 regular rhomboidal crystals of carbonate of lime. In some species 

 these crystals form an exquisite microscopic object. This state of 



