68 THE AMPHIOXUS. 



ences to be found in my observations concern the 

 employment of the first mesoblastic somite, from 

 which Kowalevsky erroneously thought that the 

 peculiar club-shaped gland took its origin. The 

 development too of the notochord I have found to be 

 somewhat otherwise. It originates, as Kowalevsky has 

 stated, from well marked folds of the hypoblast, but 

 not till somewhat later than would appear to be the 

 case according to his account. I have also in my own 

 investigation devoted more strict attention to some pro- 

 cesses at the anterior end of the embryo, to which he 

 gave but slight consideration, as well as to the further 

 increase of the mesoblastic somites at the posterior end. 



FIRST SECTION OF THE THIED PERIOD OF 

 DEVELOPMENT. 



(Formation of the Mesoblastic Somites and of the Neural 



Canal.) 



Kowalevsky describes very well for us the processes 

 of formation of the mesoblastic somites and of the 

 neural canal, which fall under this section of the 

 development. First we have a sinking of the 

 flattened dorsal side of the gastrula. The base 

 of the furrow which originates in this way is 

 overgrown by its sides. The neural plate is 



