76 PROCEEDINGS OF THE ACADEMY OF [1893. 



The well-known experiments of Dareste in artificially producing 

 monstrosities during the incubation of bird's eggs, are also well 

 known, as well, as his methods of experiment, which consisted in 

 shaking the eggs, varnishing a portion of the shell or placing them 

 in an abnormal position, upon one end, for example, during the 

 early days of incubation. Similar experiments have also been made 

 by others, that abundantly confirm the conclusion that abnormal 

 conditions or absolute mechanical disturbances during segmentation 

 are the causes of such duplication of the embryo. Rauber attacked 

 the problem from a morphological standpoint and indicated in 

 some measure the method according to which the doubling occurred 

 in the germinal disk of the eggs of fishes, working upon the blasto- 

 derm of the eggs of the Pike, Esox. He showed that the embry- 

 onic axis was duplicated or triplicated, as the case might be, at the 

 border of the blastoderm. That the distance apart of the two con- 

 temporaneously developed embryos along the rim of the blastoderm, 

 determined the degree to which their axes would be ultimately fused 

 or distinct when the larval development had been completed. 



In the study of a series of double monsters of the common lobster, 

 Homarus Americanus, I found that some similar law applied in some 

 way, but unfortunately the very early stages were not seen, so that 

 it could not be formulated with precision. The evidence for the 

 existence of such a law was, however, sufficiently complete to war- 

 rant certain general deductions, since various degrees of fusion were 

 seen which were perfectly parallel to those of fishes, except that 

 instead of the ventral aspects being fused where the rudiments of 

 the embryo had been first formed at 180° apart on the blastoderm, 

 it was here the dorsal aspects that were fused, a fact which is as 

 strictly in conformity with the morphology of the Arthropod series, 

 to which the lobster belongs, as the fusion of the ventral aspect of 

 the embryo of vertebrates is in conformity with the morphology of 

 the adult vertebrate body. 



The discovery of Kleinenberg that the embryos of certain earth- 

 worms studied by him, were sometimes double and coherent, shows 

 that such a method of double development is widely distributed 

 within the series of Bilateralia or bilaterally symmetrical animals. 



Such a budding or division in the embryo may indeed be looked 

 upon as somewhat akin to the development of buds or gemmre in 

 the Porifera or the statoblasts of certain fresh-water Bryozoa which 

 normally develop double embryos directly from a germinal body. 



