Vis- 2. 



Fig. 1 efter ran Bciicden I Fig. 2 efter ran Beneden 

 Ofl JitVni, af Karscltelf-Hei- o;/ Jnl/n, af KorsclieJt-Hei- 

 ders lærebog. ders lærebog. 



ec = ektoderm, eii = entoderm, h = blastoporus, cJi - aii- 

 lægget til chorda, n = anlægget til centralnervesystemet. 



Begge figurer viser tydelig den typislce gastrulaform. 

 Fig. 2 fremstiller et noget ældre stadium end fig. 1, og 

 her er gastrulamunden bleven væsentlig mindre. Man iagt- 

 tager desuden her, at enkelte celler, cli, har begyndt at 

 sondre sig som det første, fælles anlæg til chorda og meso- 

 derni, medens desuden i ektodermen de celler, der omgiver 

 gastrulamunden, viser sig som det forste synlige anlreg til 

 centralnervesystemet, medullarpladen. Den videre udvikling 

 illustreres nu af figurcrne 3— 5, der ligeledes fremstiller 

 mediansnit af 3 forskjellige stadier. 



Fig. 1, after ran Beneden 

 and Jalin. from KorscheU- 

 Heiders text-book. 



Fig. 2, after ran Beneden 

 and Jidin, from KorscJielf- 

 Heiders text-book. 



CC = ectoderm, en = endoderm, h = blastopore, ch = inci- 

 pieut notochord, n = incipient central organs of nervous 

 system. 



Both figures show distinctly the typical gastrula form. 

 Fig. 2 represents a rather more advanced stage thau fig. 

 1, and the gastrula aperture has become virtually smaller. 

 It will also be observed here that certain cells, di. have 

 begun to separate themselves as the first common rudiments 

 of the notochord and mesoderm, vvhile in the ectoderm, 

 the cells surrounding tlic gastrula aperture appear as the 

 earliest visible rudiments of the central organs of the ner- 

 vous system, the medullary plate. Tlie further development 

 is illustrated by figs. 3 — o, \vliicli also represent median sec- 

 tions of o different stages. 



Jip 



rier. ;i. 



Fi?. 4. 



Fig. 3, 4 og 5 efter ran Beneden og Julhi af Kor- 

 schelt-Heiders lærebog, ec = ektoderm, en = entoderm, d = 

 tarmcavitet, ch = anlæg til chorda. )i = anlæg til centralncrve- 

 system, np = neuroporus. 



Figs. 3, 4 and 5 after ?•«« Beneden and Jalin from 

 KorselieJt-Heider s text-book. ec = ectoderm, en = endoderm, 

 d = intestinal cavity, cJi = rudiment of notochord, n = rudiment 

 of central organs of nervous system, np = neuropore. 



