250 STUDIES IN GENERAL PHYSIOLOGY 



certain organs, but the specific reactions of an organ toward 

 light and gravity are also dependent upon the nature of its 

 substances. It might be believed, therefore, that the polyp- 

 forming substances also determine positive heliotropism, 

 while the root-forming substances determine negative heliot- 

 ropism. These circumstances might therefore explain the 

 apparent paradoxes in the reaction of Sertularia to light. I 

 hope to be able to study this question experimentally, and 

 therefore will not enter into any further theoretical dis- 

 cussion. 



2. I mentioned in the previous volume of these studies 

 that Bonnet and Dalyell had found that an organ of another 

 kind may occasionally grow in place of one that has been 

 lost. Dr. A. von Heider, of Gratz, called my attention to the 

 fact that he, too, had observed and described such a case. 1 I 

 will give his description in full here : 



I have often had the opportunity of testing in Cladocora the 

 great powers of reproduction which Crelenterates in general are 

 known to possess. Without discussing the rapid healing of wounds 

 and the renewal of wornout portions of the body, the following case 

 seems worthy of description. I cut off by a rapid incision, and as 

 near the rim of the shell as possible, the polyp of a Cladocora, 

 which was protruding a great distance beyond its shell, and 

 allowed the animal to go on living in the aquarium. As early as 

 the next day the tentacles of the animal, which had been robbed of 

 its calcareous support, were entirely unfolded, the transverse 

 wound at the opposite end had puckered to a conical scar, and the 

 polyp moved over the bottom of the vessel by means of its ten- 

 tacles. When examined with a lens some weeks later, the aboral 

 end of the animal was completely healed and possessed of a plate 

 running parallel to the oral plate, at the periphery of which were 

 tiny elevations corresponding to the tentacles of the oral plate. In 

 the course of two months these developed into full-grown ten- 

 tacles. In the center of this new plate of tentacles was a round 

 opening, the newly formed mouth, so that an entire oral plate had 

 been formed at the cut end of the polyp, which differed in external 



i A. VON HEIDER, Wiener Sitzungsbertchte, Vol. LXXXIV, Part I (1881). 



