4 



G. O. SARS. 



[No. 8. 



of them the ova in process of development; and, although the 

 development certainly was very slow, on the 18th of May two 

 small Daphniæ were successfully hatched in one of the jars, and 

 moved about quickly in the water. They lived, however, but 

 a few days, when they sunk to the bottom and died long before 

 attaining their full growth. Thus, from the first series of my ex- 

 periments, I succeeded only in tracing the development of the win- 

 ter-eggs of a species of Daphnia, and in examining the earliest 

 stage of the young of that form (se PL 1, fig. 10). The latter 

 exhibited however an aspect so peculiar as at once to define 

 them as a new and most interesting species. 



The reason that precluded the experiments from being ad- 

 vantageously continued in the manner specified above, was found 

 to be the water in the small jars becoming after some time 

 putrid, thereby giving rise to an infinity of Bacterians, spreading 

 over the surface like a thin film and thus preventiug the neces- 

 sary aération of the water. With a view to prosecute my 

 researches with greater certainty and more complete results, I 

 found it indispensible to work with the aid of superior apparatus. 

 In place of the small jars at first employed, I made choice of 

 larger glasses and 3 quadrangular aquaries of different sizes, the 

 largest of which had a length of nearly three feet by a breadth 

 of one foot and a half. In this latter aquary I placed the greater 

 quantity of the mud received, and in the others correspondingly 

 smaller portions. Into all I poured a sufficient quantity of waten 

 taking care that none of them should be more than half-full. Very 

 soou, however. I found that even with this improvment putrifica- 

 tion of the water, combined with a rapid development of Bacte- 

 rians, could not be prevented, and of course it was absolutely 

 necessary without delay to devise some remedy against this 

 fatal detriment. By placing in the aquaries fresh-water Con- 

 fervæ and other plants known to thrive in water, I felt sure 

 of thus putting a quick stop to the progress of putrification ; 

 and, although the accidental introduction into my aquaries 

 of ova of indigenous Entomostraca could hardly with absolute 

 certainty be avoided, I had little fear this would cause any 



