590 E. W. MACBRIDE. 



7) may be considered together. In these the segmentation of 

 the egg and the formation of the blastula and the process of 

 invagination are described. Kowalevsky states that the blasto- 

 pore is at first posterior in position, but becomes later shifted 

 on to the dorsal surface; he describes the formation of the 

 central nervous system and its appendix, the neurenteric canal. 

 He also describes the formation of the coeloraic pouches 

 (myotomes) as folds of the gut wall, and notes the fact that 

 the first pair have thinner walls and a wider cavity than the 

 rest, and communicate by a broader slit with the gut cavity. 

 He likewise gives an account of the larval life of Amphioxus, 

 and it is interesting to note that in his second paper (7) he 

 anticipated the results which Lankester and Willey obtained 

 later (9 and 13) as to the development of the gill-slits and the 

 formation of the atrial cavity. The two longitudinal ridges, 

 which by their union form the atrial cavity, were seen and 

 figured by him, and the cavities they contained also described. 

 His account of the gill-slits appeared, however, so extra- 

 ordinary to his contemporaries, that it was supposed he was 

 misled by pathological specimens, and it needed Dr. Willey's 

 researches to convince zoologists of its accuracy. 



A year or two after Kowalevsky's second paper was pub- 

 lished Professor Hatschek undertook a re-investigation of the 

 subject, and the account given of the development of Am- 

 phioxus in Korschelt and Heider's ' Lehrbuch der Vergleichen- 

 deuEntwickelungsgeschichte' is taken directlyfrom Hatschek's 

 paper. Hatschek confirmed in his first paper (3) Kowalevsky's 

 account of the segmentation of the egg ; but with regard to 

 the invagination he asserts that the blastopore is from the first 

 in its definitive dorsal position, or, what comes to the same 

 thing, that the closure of the blastopore is mainly eff'ected by 

 the backward growth of the dorsal (anterior) lip. 



This statement has been seized on with avidity by certain 

 workers in Vertebrate embryology as affording a possibility of 

 twisting the developmental history of Amphioxus into accord- 

 ance with theories which regarded the main developmental 

 process in Vertebrates as a concrescence of two distinct halves 



