INTRODUCTION. 5 



followed by his famous and exhaustive treatise 011 the 

 development of the Amphioxus lanceolatus}- 



This treatise presents us with a picture of the 

 procedure of development taken as a whole, together 

 with many details of interest. More especially it 

 makes us acquainted with the segmentation, and the 

 formation of the gastrula in the Ampliioxus, as well as 

 with the remarkable organization of the unsj^mmetri- 

 cal larvae. Furthermore, in this work the meaning 

 of the atrial cavit}', hitherto indicated as the body 

 cavity, was made plain to us. This means a con- 

 siderable advance in the understanding of the 

 comparative anatomy of the animal. 



Some very important points were not stated 

 accurately in this first treatise, and were corrected 

 by the author in another of no less importance, which 

 forms a valuable supplement to his first publications. 

 This treatise was published among the writings of 

 the Naturalist Society in Kiew. 2 Its contents, how- 



1 A. Kowalevsky, " Entwicklungsgeschichte des Amphioxus 

 lanceolatus," Mem. de Vacad. imp. desc. de St. Petersboury, 

 1867. 



2 A. Kowalevsky, " Zur Entwickhmg des Amphioxus (neuere 

 Studieu)," Schriften der Naturforschergesellschaft in Kiew, 

 Band 1, pag. 327. 1870. 



