242 Analytical Notices of Books. 



phical botanists of the day, they have become aware that the ovum, both 

 before and after impregnation, undergoes a variety of changes hitherto 

 quite unsuspected, and capable of throwing a new and valuable light, not 

 only on many of the darkest points of physiology, but also on the com- 

 plicated chain of natural affinities. They have consequently endeavoured 

 to trace the the structure of the egg from its first formation in the ovary, 

 through all its phases, to the complete developeraent of the animal to 

 which it is destined to give birth ; and thus to lay a firm foundation for 

 the determination of the general laws of organic developement. 



Among the most successful of these investigators, we may mention 

 Herold and Von Baer, to the former of whom we owe an extensive series 

 of observations on the the ova of Spiders, while the latter has devoted his 

 attention more particularly to those of Vertebrated Animals. The present 

 authour, Dr. Rathke, was stimulated by the work of Herold to follow in 

 his footsteps, and to ascertain, by the examination of one of the higher 

 order of Crustacea, to what extent its original structure and subsequent 

 developement corresponded with the remarkable peculiarities observed in 

 the nearly related tribe. For this purpose the common river Crawfish, 

 f^stacus jiuviatilis, Fab.,) appeared to offer a favourable object, on 

 account of the large size of its eggs, the lengthened period of their 

 developement, the transparency of their envelope, and the facility of 

 procuring them at almost every season. The authour gives the result of 

 his observations during the springs and summers of three successive years. 

 These observations were not, however, made on the progeny of a single 

 Crawfish, but on eggs taken successively from numberless individuals 

 brought to the market of Dantzig from the same locality; their continuity 

 therefore is not altogether complete. The magnifying instruments used 

 were either a simple lens, or one of Frauenhofer's compound micros- 

 copes ; but the latter could not have been frequently necessary, as by far 

 the greater number of the accompanying figures are magnified only fif- 

 teen times in their diameter. 



The authour divides his work into eight sections. In the first, he gives 

 a general description of the sexual organs of the full grown Crawfish, 

 which it is unnecessary here to repeat, those parts having been already 

 well described and figured by Roesel and Suckow. He then proceeds to give 

 an account of the formation of the ova, and the changes which they undergo 



