BIOLOGICAL STUDIES ON CORYMORPHA. IV. 1 



BUDDING AND FISSION IN HETEROMORPHIC PIECES AND THE 



CONTROL OF POLARITY. 



HARRY BEAL TORREY. 



The large solitary hydroid Corymorpha exhibits the phenome- 

 non of heteromorphosis in forms even more striking than those 

 under which it appears in the related Tubularia. At the same 

 time, its normal polarity is in several respects more obviously 

 marked. As against a stem ; in Tubularia, that presents little 

 or no indication of axial differentiation, the column of Corymorpha 

 is divided into several regions sharply characterized by differences 

 in form, structure and function. Its diameter varies, being 

 greatest near the base, which is enveloped, for about one third 

 the total length, in a thin layer of perisarc. Beyond the edge 

 of the latter, the naked ectoderm is thicker, its cells are more 

 narrowly columnar, and there is a marked increase in the number 

 of nematocysts. Within the perisarc is the zone of frustules, or 

 rootlets, that form the holdfast and have been homologized with 

 the stolonal processes of Tubularia, although they are far more 

 specialized structures. The proximal extremity, conical in form, 

 is furnished with an amoeboid ectoderm, by means of which the 

 polyp creeps about. 



Not only in structure does one find evidence of regional dif- 

 ferentiation, but in capacity for regeneration as well. A hy- 

 dranth is replaced after section of the column, with a velocity that 

 decreases wdth the distance from the distal end of the intact 

 hydroid. The differences in velocity are so slight as to be ap- 

 preciated with difficulty in the distal half of the column, but are 

 easily recognizable in a comparison of rates of regeneration in 

 distal and proximal thirds. Furthermore, heteromorphosis, 



'Contribution 32 from the Laboratory of the Marine Biological Association of 

 San Diego. Preceding numbers of the Biological Studies on Corymorpha have 

 appeared as follows: I., C. palma and Environment, J. E. Z., i (1904), p. 395; 

 II., The Development of C. palma from the Egg, Univ. Calif. Publ. Zool., 3 (1907), 

 p. 253; III., Regeneration of Hydranth and Holdfast, ibid., 6 (1910), p. 205. 



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