276 WILLIAM A. KEENER. 



If this conclusion is correct and if the nematocysts of aeolids 

 are derived from ccelenterata, the question can be raised, among 

 many other more subtle ones, have the seolids acquired their 

 method of dealing with nematocysts of coelenterata through 

 flatworm ancestry, or are these cases of parallel development of 

 reflexes or instincts? 



I hope to be able to make a series of experiments upon the 

 nematocysts of these Rhabdocceles. 



SUMMARY. 



The nematocysts of Microstoma are derived from Hydra upon 

 which Microstoma feeds. These ingested nematocysts are de- 

 livered to the mesoderm by the endoderm of the flatworm. 

 Within the mesoderm an amoeboid cell takes charge of each 

 nematocyst and as it is transported to the surface orients it 

 so that the " sting- thread " has its discharging pole directed 

 towards the exterior of the animal. Thus Microstoma has come 

 to use the nematocysts of its prey as do the aeolids use the 

 nematocysts of their prey. 



BIOLOGICAL LABORATORY, 



UNIVERSITY OF VIRGINIA, 

 March, 1911. 



BIBLIOGRAPHY. 

 Boulenger, Charles L. 



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Quart. Journ. Mic. Sc., N. S., No. 220, Vol. 55, Part 4. 

 Conklin, E. G. 



'08 Two Peculiar Actinian Larvae from Tortugas, Florida. Pub. Carnegie 



Inst., Washington, D. C., No. 103. 

 Glaser, Otto C. 



'09 The Phj-siology of Nematocysts. Journ. Exp. Zool., Vol. 6, No. 3. 

 '10 The Nematocysts of Eolids. Journ. Exp. Zool., Vol. 9, No. i. 

 Graff von, L. 



'82 Monographic der Turbellarien. 

 Grosvenor, G. H. 



'03 On the Nematocysts of ^Eolids. Proc. Royal Soc., Vol.*2. 

 Hadzi, J. 



"07 Ueber die Nesselzelhvanderung bei den Hydroidpolypen. Arb. Zool. 



Inst. Wien., Tom. XVII. 

 Hallez, P. 



'79 Contributions a 1'Histoire naturelle des Turbellaries. Lille. 



