432 Fuchs, The effect of abundant food on the growth of young Ciona intestinalis. 



Now there were several factors which were different in the 

 food jar and in the aquarium and which might account for the 

 difference in growth. The temperature and lighting were the same 

 in both, as was also the salinity of the water. The three points 

 in which the conditions in the food culture differed from those in 

 the aquarium were as follows: 



(1) Abundance of food (algae). 



(2) Volume and lack of motion of water. 



(3) H-ion concentration of water. 



Further experiments were accordingly made to decide to which 

 of these factors the observed effects were due. 



The third factor mentioned requires a word of explanation. It 

 was found by employing Sorensens colorimetric tests 2 ) that the H-ion 

 concentration of the water in the jar containing abundant growths 

 of green algae (used in Series II) was considerably less than that 

 of the water circulating through the aquarium. The former gave 

 green with a-Naphtholphthalein and the latter faint green. Again, 

 the former gave rose with Phenolphthalein and the latter no colour. 

 It was then found by tests with both these indicators that the ad- 

 dition of I drop N/10 NaOH to 10 ccm aquarium water gave a 

 solution less alkaline than the weed water, while the addition of 

 2 drops gave slightly more alkalinity than the latter. 



In the experiments illustrated by the photographs of Series III, 

 aquarium-grown animals, of which Fig. 7 (9/11 nat. size) is typical, 

 were employed. The photograph was taken on Mar. 19th , when 

 the animals were about three months old. On this date some of 

 the animals were removed to each of three jars containing equal 

 volumes of, 



(1) aquarium water, the sides of the jar being coated with 

 abundant growths of green algae; 



(2) aquarium water, containing no additional food material; 



(3) aquarium water -)- 2 drops N/10 NaOH per 10 ccm water, 

 also with no additonal food material. 



Jar (2) tested the factors of volume and stillness of the water, 

 and jar (3) the H-ion concentration of the water, without the 

 extra food. 



It was found on Mar. 27th. (8, days later) that the animals 

 in jars (2) and (3) were absolutely unchanged as regards the ratio 

 of oral siphon to body length, being exactly similar to the individ- 

 uals left in the aquarium. Those in jar (1), however, showed the 

 typical siphon elongation of the food culture forms. A typical 

 example from this jar is shown in Fig. 8 (11/14 nat. size.) (After 

 having been photographed, this animal was replaced in the aquarium, 



2) Compt. Rend, du Lab. de Carlsberg, 1909. 



