cxlvi GENERAL SUMMARY OF SCIENTIFIC AND 



The essays by Mr. J. A. Allen on the geographical distribution of 

 certain birds and mammals, notably the bison, and the essay by the 

 writer, on the distribution of the Geometrid moths, in his monograjjli 

 of that family, are fresh contributions to zoogeography. 



In a paper on the origin of the deep-water fauna of the Lake of 

 Geneva, M. Forel thinks the entire fauna of the Swiss lakes is de- 

 scended from forms which have migrated up the rivers since the 

 melting of the glaciers, and have afterward been differentiated. 



Among recent contributions to the general subject of the embry- 

 ology of animals are two by Professor E. Van Beneden, of Liege. 

 One is on the maturation and fecundation of the egg and earlier 

 embryonic phases of the mammals, from researches made on the rab- 

 bit, and is an extension of Bischotf' s famous work on the embryolo- 

 gy of the rabbit. A second i)aj)er, on the history of the germinative 

 vesicle, is based on studies made on the common star-fish of the 

 European coast {AsteracantMon rubens). A paper of a very different 

 sort is a fierce attack on the " gastrsea " theory, by M. Moquin-Tan- 

 don, in the Annales des Sciences JVaturelles. He concludes that it 

 does not rest on any fundamental fact, and can not serve as a base 

 of a phylogenetic classification. The theory had previously been 

 attacked in the American Naturalist for February by Mr. A. Agassiz. 

 On the other hand, in the April number of the same magazine. 

 Professor Cope, in an article entitled " Progress of Discovery of the 

 Laws of Evolution," welcomes Haeckel's gastroea theory, which we 

 have previously exf)lained. Cope says that this theory has " added 

 the keystone to the doctrine of evolution in his gastraea theory." 



Several embryological papers of value have been published by 

 Balfour, who also fully indorses the gastrsea theory of Haeckel. 



Some four years ago the Rev. W. H. Dalliger and Dr. Drysdale be- 

 gan to publish a series of papers, which have attracted much notice, on 

 the life-history of monads. The last is now published. The authors 

 remark that simple conditions of season and temperature may ac- 

 count for their successive appearance in the fluid, without supposing 

 that one fonu was developed out of another. " On the contrary, the 

 life-cycle of a monad is as rigidly circumscribed within defined 

 limits as that of a mollusk or a bird." In no instance was the con- 

 tinuance of the species maintained without the introduction of a 

 sexual process, a blending of what were shown in the sequel to be 

 genetic elements. The experiments as to the efifect of heat on the 

 monads and their spores uniformly established an important fact, 

 viz., that the spores resist heat much better than tlie adults. A 

 temperature of 150 Fahr. was always found to destroy utterly all 

 the adult forms, while the spores resulting from sexual generation 

 have a power of resistance to heat which is greater than this in the 

 proportion of eleven to six on the average. " This appears to us," 

 they say, " to be the very essence of the question of biogenesis versus 



