74 ' "AS. \V. IIARC.ITT. 



import as to the negative influence of" such factor^ a< light, 

 gravity, etc., in relation to growth. This is further borne out. 

 by attention to the aspects of the several tubes which may com- 

 prise a given colony. In several such an actual count of the 

 growth direction was made. On a stone which contained 37 

 living specimens I found that 12 had a general upward direction; 

 15 had just as definite a downward course; and 10 had a hori- 

 zontal direction. Another colony growing on the inside of 

 an iron cup about 6X10 cm., made up of eleven specimens. 

 showed the following disposition as to direction: 4 upward, 5 

 directly down, and 2 horizontal. On the outside of the same cup 

 were eighteen specimens disposed as follows: 8 upward. 7 down- 

 ward, and .} horizontal. These plainly go to confirm the con- 

 clusions already drawn, that in the matter of orientation one is 

 utterly unable to discover the operation of any one or several 

 factors which are in any sense determining. 



HYDROIDES PECTINATA. 



This species and the one described in the following section, 

 Spirogaphis spallanzanii, were the ones used by Loeb in his well- 

 known experiments at Naples many years since, the results of 

 which, including also several species of hydroids, served as a 

 basis for his far-reaching theory of animal heliotropism, especially 

 as it relates to sessile animals. Naturally, therefore, more of 

 details will be expected in 'the following accounts than in the 

 preceding, and I shall endeavor to make explicit and definite 

 records both of methods and results. 



Ilydroidcs pectinata (^Serpiila uncinata) is one of the most 

 common and abundant of the Naples annelids. I nlike Spiro- 

 graphis, it grows usually in immense colonies, aggregating hun- 

 dreds or perhaps thousands of individuals. Fig. 2 will give a 

 general idea as to their appearance in small colonies. The tubes 

 of a given colony form a mass of more or less parallel aspect, the 

 individuals apparently growing at approximately the same rate 

 and in the same general direction. When one casually examines 

 such a colony it \\otild seem to afford a typical illustration of 

 orientation due to some single constraining stimulus. Hut here 

 again, as in the case cited above as to stereo tropism, extended 



