REARING OF SERPULID LARY.E. 3 I I 



material in shape to fit the body. At such a time the body may 

 project a considerable distance from the anterior end of the tube. 

 The tube is deposited quite rapidly. In the case shown in Fig. 

 2 the amount of growth in the course of twenty hours is given. 

 This is equal to .29 mm. or .35 mm. per day. 



I tried to discover some regularity in the arrangement of the 

 axes of the tubes with respect to gravity, light and food condi- 

 tions but was able to find no general rule in the 

 matter although some groups seem to be arranged 

 with respect either to maximum food-obtaining 

 ability or with respect to a lateral stimulus of un- 

 known character. Fig. I which is reproduced 

 from my notebook gives a small section of a side 

 of one of the jars. Evidently there is no general 

 rule of arrangement though radial divergence of ^ 



r 1G. 2. { y<^ 



the kind shown at a and b (Fig. i) may be ex- 3 g,) Open end 

 plained on a utilitarian basis as a spreading out of a tube of Hy- 

 from a central point in order to obtain more feed- droides ttllci ata - 



The unshaded 



ing room. The arrangement at c however does port ion represents 

 not come under this head but must be considered the amount of ad- 



as a very definite response to a lateral stimulus, dmon to the tube 



, . . in the course of 



It is hard to conjecture what this stimulus may twent hours 



have been. 



General Activities of the Young at a Later Stage. - The fol- 

 lowing observations were made on young individuals during the 

 few days preceding and the few days following the formation of 

 the operculum. Specimens of Hydroidcs uncinata and H. pectinata 

 observed at the Naples Zoological Station during the winter of 

 19021903 as well as the H. dianthns of Cold Spring Harbor 

 were used. 



The two eye spots are very prominent at this stage and a 

 sudden shadow such as is produced by the passing of a hand 

 between the animals and the source of light causes the serpulids 

 to contract and withdraw with a jerk into their tubes. The 

 branchiae are. then completely hidden inside of the tube and be- 

 fore the development of the operculum their ends form a barri- 

 cade a short distance within the opening. After a short period 

 of inaction if there is no new disturbance the fine thread-like 



