234 BULLETIN OF THE 



It is possible that Laurent had observed the so-called chalaza at the 

 time (1835) his first article was published ; but it was subsequent to 

 the appearance of a paper by Van Beneden and Windischmann, — in 

 fact after that paper was already known to him, — that he speaks ('38, 

 p. 134, foot-note), for the first time, of a "filament tortille qui existe 

 constamment dans tous les oeufs de limace." This is described more 

 at length on page 146 of the last-mentioned paper. 



Although Dumortier ('37) states in his memoir on the development 

 of Mollusks that he has studied the eggs of Limax, his results are all 

 drawn from the study of Lymnaeus ovalis. 



In the same year (1838) that the last-mentioned paper of Laurent 

 appeared, Van Beneden and Windischmann ('38) wrote of Limax 

 agrestis as follows : " As regards the composition of the egg, we have 

 found almost nothing which does not accord with the observations 

 of M. Laurent. Nevertheless, we have established the presence of a 

 ' cordon filamenteux ■ which becomes especially visible at a certain 

 epoch of development, and which appears to us to have an evident 

 analogy with the chalaza of the eggs of birds. This same cordon has 

 already been pointed out, however, in the eggs of Helix pomatia." 



In their final paper ('41, p. 6 [p. 20, £tudes], and '41^ pp. 178, 179), 

 published in 1841, these authors announced the following as the com- 

 position of the egg, from within outwards: 1st, a vitellus ; 2d, a great 

 quantity of albumen holding in suspension the "filament entortille" 

 (previously called " cordon filamenteux ") ; 3d, a delicate, transparent 

 membrane covering the albumen ; 4th, a slight layer of liquid ; 5th, a 

 quite thick exterior membrane composed of numerous layers. The points 

 of correspondence with the descriptions of Turpin and Laurent are ap- 

 parent. The clear space of the latter author is the liquid layer of Van 

 Beneden and Windischmann. The structure called " filament entortille " 

 was at first (1838) regarded by Van Beneden and Windischmann as 

 homologous with the chalaza of birds' eggs, but, from the variations oc- 

 curring in different eggs, they subsequently concluded that it was a torn 

 membrane which at first surrounded the vitellus, and that consequently 

 it really appertained to the vitelline membrane. The latter view has 

 been sufficiently refuted by Warneck ('50, p. 107). 



The description of the egg by the last-mentioned observer (pp. 105- 

 111) differs in some points from that of his predecessors. The albumen 

 is invested by two membranes, — membrana alhuminis secundaria seu 

 interna, and membr. alh. primaria seu externa. The former is easily 

 thrown into folds by compression ; the latter is much thicker than the. 



