28 Hjalmar Théel, « 



A year later Fewkes ') states with regard to the Clypeastroid 

 Echinarachaius that »with the first indication of an ingrowth of the ga- 

 strula stomach or archenteron, we find budding off into the segmentation 

 cavity certain cells»; to judge from his figures, these mesenchyme cells 

 arise from the entoderm. 



In 1888 Barrois ^) explains that the mesenchyme takes its origin 

 in Comatula mediterranea from the archenteron and mainly from its 

 end, and the same year Fleischman ') states with regard to the Spatan- 

 goids, that the wandering cells issue from the vegetative pole of the 

 Blastula of Echinocardium cordatum. Lastly in the same year Korschelt*) 

 makes known his views of this matter and asserts that the mesenchyme 

 originates from the entoderm, either from the vegetative pole of the 

 Blastula (Echinoids, Ophiurids and the genus Cucumaria), or from the 

 place which has just begun to invaginate (Holothuria), or from the end 

 of the invaginated archenteron (Asteroids, Crinoids and Synapta). 



A quite different view was suggested, first by Greeff ^) with 

 regard to Asterias rubens and afterwards by Bergh ^), who has studied 

 the first stages in the development of Echinus miliaris. Both agree in 

 the opinion that the mesenchyme arises not only from the entoderm but 

 also from the ectoderm, though Bergh adds that the greater number of 

 wandering cells issue from the former. In his splendid researches on the 

 development of Asterina gibbosa Ludwig '') comes to the general result, 



1) Preliminary Observations on the Development of Ophiopholis and Echina- 

 rachnius. 1886. p. 126. 



2) ßecherches sur le Développement de la Comatule (C. mediterranea). — 

 Recueil zoologique Suisse. IV. 4. Genève-Baie 1888. p. 552 — 554. 



3) Die Entwicklung des Eies von Echinocardium cordatnm. 1888. p. 139. 



4) Zur Bildung des mittleren Keimblatts bei den Echinoderraen. • — Zool. Jahr- 

 bücher in. 4. Jena 1889. p. 667. 



5) According to Selenka, Ludwig, Koeschelt etc. Unfortunately I have 

 not had the opportunity myself of seeing the original: »Ueber den Bau und die Ent- 

 wicklung der Echiuodermen. Sechste Mittheiluug — Sizungsber. d. Ges. z. Bef. d. ges. 

 Naturwissensch. Marburg 1879. N:o 4. p. 51 — 52». In an earlier paper: »Ueber die 

 Entwicklung des Asteracanthion rubens vom Ei bis zur Bipinnaria und Brachiolaria» 

 printed in the sagpe journal 1876, he evidently holds the contrary view, viz. that the 

 mesenchyme originates from the entoderm. 



6) Bidrag til Opfattelsen af Klovning og Kimbladdanelse hos Echiniderne. — 

 Vidensk. Meddel. fra den naturh. Foren, i Kjobenhavn. 1879—1880. p. 263. 



7) Entwicklungsgeschichte der Asterina gibbosa Forbes. — Abd. aus Zeitschr. 

 f. wiss. Zool. Bd. 37. Leipzig 1882. p, 127. 



