48 CALIFORNIA ACADEMY OF SCIENCES. 



29). It is probable that division has recently taken place 

 in such cases, though I have never noticed a cell in the 

 act of division. 



Two papers have recently appeared which call seri- 

 ously in question the view generally held by students of 

 the Tunicata that the cells of the test are of ectodermal 

 origin. The papers referred to are those of Salensky 

 ('91) and Kowalevsky ("92). The first-mentioned author 

 refers to the fact that Delia Valle has observed the wan- 

 dering out of ectodermal cells from the ectoderm into the 

 " cellulose mantel," there to become transformed into the 

 cells characteristic of this layer, and he then adds: " Ich 

 kann eine solche Auswanderung auch fur die Pyrosomen 

 gelten lassen, muss aber annehmen, dass der grosste 

 Theil der ausserhalb des Cyathozoids liegenden Zellen 

 von asgewanderten Mesenchymzellen stammt " (p. 12.) 

 " Wenn diese Zellen auswandern, so kann man sie leicht 

 zwischen den Zellen des Ectoderms erkennen, und 

 dadurch wird die Entscheidung der oben aufgestellten 

 Frage liber die Natur der ausserhalb des Embryos lie- 

 genden Zellen bedeutend erleichtert " (p. 13.) 



And the author illustrates the conditions thus described 

 by figs. 30a and 31. 



It was with special reference to this point that Kowal- 

 evsky's paper was written, and he dwells upon it in his 

 text and illustrates it in his plates so fulh^ that there can 

 be no doubt that in the larval development of Phallusia 

 mammilata the species in which he studied the question, 

 cells of the test are derived from mesenchyme cells which 

 migrate through the ectoderm. 



" Somit steht es," writes the author (p. 7), "wenigsten 

 fur die einfachen i\.scidien und speciell fur Phallusia fest, 

 dass deren Mantelzellen aus dem Mesoderm abstammen ; 

 alien Wahrscheinlichkeit nach wird sich derselbe Process 



