HAECKEL S RECENT ADDITIONS TO GASTRiEA-THEORY. 61 



Haeckel is very careful to insist on the unicellular character 

 of the Discomonerula and Discocytula, even where it attains 

 the large size seen in Birds. In his support of Gegenbaur's 

 view advanced so long ago as 1861, he will be joined by 

 most embryologists of to-day. He takes occasion to express 

 his objections to the ' parablastic theory ' of His, which I 

 may say does not appear to me to be really supported by 

 the fact which His recently quotes from my observations on 

 the ovarian egg of Loligo and Sepia ('Phil. Trans.,' loc. cit.). 

 The cells which are to be found in the ovarian egg of these 

 Cephalopods, and which have j)assed into it from the cell- 

 lining of the egg-capsule (granulosa), are not in such a state 

 as to lead one to suppose that they are capable of development. 

 They are, as Haeckel insists, passive nutritional material. 



The invagination of the disc-like morula in the discoblastic 

 type, to give rise to the Randwulst or Properistoma (blasto- 

 pore-margin) is a fact of great importance, which Haeckel 

 attempts to illustrate in other vertebrate forms besides the 

 osseous fish, in which he observed it with care. The diagrams 

 (figs. 41 to 54) serve to explain these views, which the reader 

 may compare with those advanced by Mr. Balfour in this 

 Journal, July, 1875. 



The origin of the mesoblast in his marine osseous fish 

 Haeckel did not satisfactorily determine. It appears, how- 

 ever — a fact on the general importance of which, as above 

 mentioned, Haeckel insists — that it first makes its appearance 

 in the Randwulst (blastopore-margin), and is, he believes, 

 traceable to delamination from the ectoderm (epiblast), and 

 also to delamination from the endoderm (hypoblast). The 

 first portion (Hautfaserblatt^) has a bilateral symmetry, gives 

 rise to the so-called ' protovertebrse,' and corresponds to the 

 bilaterally symmetrical commencements of mesoblast, which 

 Carl Rabl has observed in Limnseus, and which are charac- 

 teristic, according to him, of all the Bilateria (that is to say, 

 the Vermes and the four great types connected with them). 

 The second portion, which comes from Hypoblast, consists of 

 a layer of hypoblast cells and of amoeboid cells of very active 

 movement, which wander between spaces in the hypoblast 

 and spread themselves partly on the surface of the yelk and 

 partly in the embryo itself. They give rise to blood cells, 

 connective-tissue cells, and pigment cells. The outer layer of 

 hypoblast cells and these amoeboid cells Haeckel considers 

 as the Darmfaserblatt." He lays especial emphasis on the fact 

 that this set of cells do not have a bilateral arrangement pri- 



' Hypoderon or hypoderic cell-layer. 

 ^ Hypenteron or hypenteric cell-layer. 



