469 



als WoLTERECK bei Polygordius^ womit sie grosse Uebereinstim- 

 niung aufweisen. Nahere Bestatigung seiner nicht ganz entschie- 

 denen Angabe ware denn auch nicht überflüssig. 



Für Hydroides {Eupomatus) imdnatus giebt Shearer (1911) 

 über den Blastoporus an: „When fully formed it is an elongated 

 slit, somewhat enlarged at its anterior end. This end never com- 

 pletely closes, but after the formation of the stomach becomes 

 the future mouth. The posterior portion closes completely, the 

 anus breaking through almost immediately at the point where 

 the last portion of this part of the blastopore disappears. Thus 

 the closure of the blastopore in Eupomatus is essentially the same 

 as in Pohjijordius^ although the different steps in the process are 

 not so evident." 



Auch bei Thalassema ist nach Torrey (1903) der Blastoporus 

 ,,an elongated slit with an enlargement at the anterior end. This 

 part never closes, but after the formation of the oesophagus be- 

 comes the mouth The posterior part of the blastopore finally 



becomes closed by the approximation of the sides." Über die Bil- 

 dung des Anus sagt Torrey : ,,The anus itself breaks through 

 very late, even after the trochophore] has begun to feed." Die 

 Angabe Conn's „that the anus is formed at a point which cor- 

 responds to one end of an elongated][blastopore" nennt er in einer 

 Anmerkung „true only in the most general sense", ohne dass sich 

 in diesem Fall offenbar genauerc Angaben darüber machon lassen. 



Eine klare Darstellung der Gastrulationsvorgange, wie wir sie 

 bei den bis jetzt untersuchten Anneliden in der Regel begegnen, 

 giebt Mead für Amphitnte in der folgenden Weise : 



„The manner in which the somatic plate extends into the ncw 

 area is of especial interest. Upon the invagination of the meso- 

 derm, the posterior border of the somatic plate moves slightly 

 backwards, and meets the entoderm plate at the center of the 

 subumbrella, — the point 5, Textfig. VII, A, B. This is the 

 only backward movement which occurs on the border of the 

 somatic plate in the middle line. The material at h always remains 

 90° from the prototroch, and finally becomes the posterior end 



