The Relations between Marine Animai and Vegetable Life. 409 



In the four experiments made with water exposed to the sun 

 for four or more days in a covered jar, there is an average diminu- 

 tion of 4.5^ in size. As the numbers are very variable, little relianee 

 can be placed on this result. On the other band, with water exposed 

 to the siin in a flask filled up to the neck, a negative etfect was 

 produced in each case, this amountiug on an average to 10.4^. In 

 that the body lengths in these particular experiments were found to 

 increase on an average by 16.7^, it follows that there was still an 

 increase of 6.2^ in the absolute arm length. 



With water purified by beiug kept in darkness for some weeks, 

 the increase in arm length is very marked, it amounting on an 

 average to 16.5^. The increase in body length in these particular 

 experiments averaged 7.5^, hence the arm tissues bave reacted 

 much more than the body tissues to the environmental change. With 

 water filtered through asbestos there is also a slight increase in arm 

 length, though the figures are too variable to place much relianee 

 in. A previous heating of the water has, on the other band, a totally 

 dififerent influence upon the growth of the arm and of the body tissues 

 Thus we bave previously seen that larvae grown in water heated to 

 100° bave their body lengths increased by 6.9^, and those in water 

 heated to from 50" to 77", by 5.6^. The arm lengths on the other 

 band are diminished by no less than 25.3^ with water heated to 

 100° but are practically uninfluenced by water heated to 77°. This 

 seems at first sight an almost inexplicable result, as indeed to severa! 

 of the other results arrived at, but probably they may ali of them 

 rightly be ascribed to the effects of bacterial growth. Thus in the 

 former paper it was shown that in these larvse the first stages of 

 body growth are very much more rapid than those of the arm growth, 

 whilst later on the reverse is the case. For instance, at the end of 

 the third day the body bas grown to 90.6^ of the length it will 

 attain on the eighth day, whilst the anal arm has reached only 

 63.8^. It follows therefore that if the tissues of these larvse are 

 afifected by bacteria at ali, those of the body will be most influenced 

 by the bacterial condition of the water during the first two or three 

 days of development, and those of the arms by its condition on 

 the subsequent days. For instance, in these experiments on the 

 etfects of previously heating the water, the water must at first 

 bave contained much fewer bacteria than the normal tank water. 

 On the second day, however, it was found that the numbers of 

 bacteria in the heated water were on an average the same as 



