448 KANSAS CITY REVIEW OF SCIENCE. 



which lead an independent Hfe. In such cases as these external conditions act upon 

 the larvae as they do upon the mature form ; hence we have two classes of changes^ 

 adaptational or adaptive, and developmental. These and many other facts must 

 be taken into consideration ; nevertheless naturalists are now generally agreed 

 that embryological characters are of high value as guides in classification, and it 

 may, I think, be regarded as well-established that, just as the contents and se 

 quence of rocks teach us the past history of the earth, so is the gradual develop- 

 ment of the species indicated by the structure of the embryo and its developmental 

 changes. 



When the supporters of Darwin are told that his theory is incredible, they 

 may fairly ask why it is impossible that a species in the course of hundreds of 

 thousands of years should have passed through changes which occupy only a few 

 days or weeks in the life-history of each individual ? 



The phenomena of yolk-segmentation, first observed by Prevost and Dumas, 

 are now known to be in some form or other invariably the precursors of embry- 

 onic development; while they reproduce, as the first stages in the formation of 

 the higher animals, the main and essential features in the life-history of the lowest 

 forms. The "blastoderm" as it is called, or first germ of the embryo in 

 the egg, divides itself into two layers, corresponding, as Huxley has shown, 

 to the two layers into which the body of the Calenterata may be divided. Not 

 only so, but most embryos at an early stage of development have the form of a 

 cup, the walls of which are formed by the two layers of blastoderm. Kowalev- 

 sky was the first to show the prevalence of this embryonic form, and subsequent- 

 ly Lank ester and Haeckel put forward the hypothesis that it was the embryonic 

 repetition of an ancestral type, from which all the higher forms are descended. 

 The cavity of the cup is supposed to be the stomach of this simple organism, and 

 the opening of the cup the mouth. The inner layer of the wall of the cup con- 

 stitutes the digestive membrane, and the outer the skin. To this form Haeckel 

 gave the name Gastrsea. It is, perhaps, doubtful whether the theory of Lankester 

 and Haeckel can be accepted in precisely the form they propounded it ; but it has 

 had an important influence on the progress of embryology. 



[ To be Continued ] 



INDUSTRIES OF SWEDEN AND NORWAY. 



Although in Norway and Sweden there are many mines and mills, most of 

 the people gain their living either out of the soil or the sea. The farmer in either 

 country is a marvel of industry and thrift; he would live upon what an American 

 farmer wastes, and live more comfortably than our farming population do, as a 

 rule. The amount of labor performed at the special dairy farms, to which cattle 

 are driven in summer, generally by girls, would horrify a western maiden; but 

 the Swedish and Norwegian girls thrive on it, enjoying rare good health and 



