270 WILLIAM A. KEPNER. 



The question at once arises, might not this nematocyst have 

 wandered from the mesoderm into the endoderm? There is 

 ample evidence of nematocysts migrating from one region to 

 another in the bodies of coelenterata. Schneider says: "Alle 

 Nesselzellen...der Siphonophoren enstehen an localisierten Bil- 

 dungsherden, von denen sie in einen bestimmen Entwickelungs- 

 tadium als Wanderzellen auf die Verbrauchstatten uberwandern" 

 (Boulenger, 1910, p. 764). In this connection "Hadzi's results 

 are of the greatest interest, as he was able to examine living 

 tissue as well as preserved material. His main conclusions are 

 as follows: 



"i. The thread-cells of hydroids are not formed 'in situ' 

 but in the ectoderm of the ccenosarcal branches, where, on ac- 

 count of the thick perisarcal investment, they can obviously 

 not become functional. 



"2. When completely developed, except for accessory struc- 

 tures such as the cnidocils and the stalks, they migrate to the 

 important nematocyst batteries on the tentacles. This migra- 

 tion can take place in two different manners. In simple forms, 

 e. g., Campannlaria, the thread cells move actively by means of 

 their pseudopodia, making their way between the ectodermal 

 cells of the colony. In Tubularia, however, they adopt a quite 

 different method of locomotion : from the ectoderm of the ccenos- 

 arc they force a way through structureless lamella and endoderm 

 into the cavity of the hollow stem, whence they are carried by 

 the current caused by the flagella of the endoderm cells to the 

 hydranths. Here the thread-cells re-enter the tissues and 

 migrate actively by their own movements to the ectoderm of the 

 tentacles" (Boulenger, 1910, p. 764). Conklin (1908) likewise 

 observed the formation of nematocysts \vithin the mesoderm of 

 Actinia and their subsequent migration to the ectoderm. Bou- 

 lenger states "that in Mcerisia the nematocysts of the oral 

 battery of the medusa are developed in the endoderm at the base 

 of the manubrium ; this does not necessarily imply that the nemato- 

 blasts are themselves of endodermal origin" (Boulenger, 1910, 

 p. 767). Thus we have much testimony as to the migration of 

 nematocysts within the tissues of coelenterata. 



It is to be noted, however, that in all these cited examples the 



