19 



stapen of rropress; a-d ir Figure 21 the endoderi?al tisnue 

 has filled 'he entire cavity. 



/.ccordinp to ; etschnilrrff , i- his descrirticr of uni- 

 rclar injures si en or "hyrctro-e, " the erdoder^-al tissue 

 arise? as a rule by bodily ■■iFroticn of endoderral cellr irtn 

 the blastocreie, and net by a transverse division of the 

 ectodermal cells — the inner rarts pcinp to fcr^ erdoderr 

 and the outer narts re-aininp as ectoderral cells. In 

 Figure 2C, Plate 2 ;.'etschnil:off shows a cell in -,he nrc- 

 cess of tra-^sverso division"; ar^r in Finure 21 of ihe sa^e 

 Plate tv/c cell;? are so situate(" that one can easily i-^fer 

 that they riay have a'.'^isen hy transverse division of a sinple 

 ectoderT-a" cell, Thene flpurer- are of Clytia a'-d i'^ his 

 descrintir" of the saTe sr.ecies he rro'-tli^ns the '^ell in Fig- 

 ure 20 as the O'^ly one that he r'ound in which transverse 

 division- occured. This he seers to regard as an exception , 

 and claims that as a rule the ectoder'^al cells increas- by 

 longitudinal division and rrigrate i^-to the interior. 



