304 G. H. PARKER 



I, therefore, spent a large part of the summer of 1916 studying 

 the structure and reactions of Corymorpha. My work was done 

 at the Scripps Institution for Biological Research, La Jolla, 

 and I am under obligations to the Director of the Institution, 

 Dr. William E. Ritter, and to his staff for unfailing assistance 

 and many courtesies. 



It might seem superfluous after the very able work that 

 Torrey ('02, '04 a, '04 b, '05, '07, '10 a, '10*b, '10 c) has done 

 on Corymorpha to undertake a study of the reactions of this 

 animal, but my objects were somewhat different from those 

 that Torrey had in view and, though I went over much of the 

 ground that he covered and confirmed most of what he did, 

 I believe I have brought to light some new facts that add to 

 our knowledge of the natural history of this most interesting 

 species. 



2. REACTION SYSTEMS 



Corymorpha palma is a beautifully transparent, solitary 

 hydroid of slender proportions. Its stalk measures as much 

 as 10 cm. or more in length with a diameter at the thickest 

 part of about 0.5 cm. Its proximal end is anchored in the 

 mud and its distal end carries a hydranth that when expanded 

 may have a spread of 2.5 cm. The proximal portion of the 

 stalk ends in a blunt point and carries rows of long filamen- 

 tous bodies, the frustules, by which it is anchored in the mud. 

 This portion of the stalk, often half a centimeter or so in 

 length, is commonly turned nearly at right angles to the rest, 

 which is held vertically above the mud. A little above the 

 level at which the stalk emerges from the mud it gains its maxi- 

 mum diameter; distal to this it becomes gradually more and 

 more slender till it reaches a narrow neck, on which the hy- 

 dranth is borne. The stalk itself is marked by a series of lon- 

 gitudinal canals inbedded in its more peripheral substance and 

 running for the most part parallel to each other except toward 

 the proximal end, where irregular cross fusions are common. 

 The proximal third of the stalk is covered with a thin perisarc, 

 the rest being naked. 



