114 whitman: " [Vol. I. 



respecting the genetic relations of the germ-layers. Even 

 Hoffmann (No. 4, p. 45), working as late as 1877, with " Pikro- 

 carmin gefarbten Querschnitten," arrives at the same conclusion, 

 and expresses it in words that appear to be, in great part, a 

 direct transcript of Leuckart's phraseology. 



According to Robin (No. 5, pp. 297-298), the entoderm 

 arises as a solid cord of cells in the axis of the mass rep- 

 resented by the three entoblasts, a, b, and c. A lumen 

 first appears in the oesophageal portion of the axial cord, 

 and is gradually extended backward, thus forming a digestive 

 tube, with all the yolk lying external to it. Somewhat later 

 (5-8 days after exclusion) the three entoblasts (" globes 

 vitellins") undergo cleavage, breaking up into large cells, that 

 form " la coiicJie inoyenne de Vintestin et particular emetit la 

 coucJie hepatiqne!' 



In my memoir on " the Embryology of Clepsine " I was 

 unable to give a complete history of the origin of the mesen- 

 teron from the three entoblasts, but the facts there presented 

 appeared to leave little room for doubt. Both my observations 

 and conclusions have been contradicted by one of the latest 

 writers on the subject. Soon after the publication of my paper 

 came Hoffmann's (No. 6) second contribution to the embryology 

 of the Hirudinea, in which he declares his opposition to my 

 views in the following words : " Ich muss dieser Entstehungs- 

 weise des Darmepithels auf das bestimmteste wiedersprechen. 

 Die ' dark spots in the opaque yolk,' welche nach Whitman in 

 der Zeit, dass die Keimstrange sich ausbilden, so recht deutlich 

 auftreten, sind, ich vviederhole es, nichts andere's als Protoplasma- 

 Masse, welche sich aus dem Deutoplasma neu gebildet hat, sich 

 abschniirt und so an der Bildung der Keimstrange sich 

 betheiligt. Bei aitsgeschlilpften Embryonoi findct man inner- 

 halb des Dotters a^ich nicJit einen Kern. VVaren sic vorhanden, 

 so miissten sie an in Pikro-carmin gefarbten Schnitten sichtbar 

 werden, denn die intensiv rothe Farbe der Kerne und des Proto- 



(4.) Hoffmann, C. K. Zur Entwickelungsgeschichte der Clepsinen. Niederllind- 

 isches Archiv fur Zoologie, IV., H. I, p. 31. 18S7. 



(5.) Robin, C. Memoire sur le Developpement Embryogenique des Hirudinees. 

 Paris. 1875. 



(6.) Hoffmann, C K. Untersuchungen Uber den Bau und die Entwickelungsge- 

 schichte der Hirudineen. Haarlem. 18S0. 



