Phjllopod Crustacea. 333 



1st of August, I fouud eiglit of them partly filled with water, 

 in six of wliieh the xlrtctaia' were fouud in abundance, though 

 more numerous in one than ni any (jf the others. In one tub, 

 in wliieh the water had a decidedly milky a})pearance, they 

 were so abundant that hundreds could be obtained in a few 

 minutes. The water in some of the other tubs containing them 

 was of a reddish or brownish hue, or about the colour of weak 

 tea. In two no xirteiauv could be seen ; and in these the water 

 ap[)eared to have been more recently renewed. Search was 

 made in tlie pools from which the water had been taken ; but 

 no Artemiai were found, though doubtless from these places 

 the progenitors of those inhabiting the tubs must have been 

 taken. It is probable that in the pools they exist in very 

 small numbers, being kept in check partly by various small 

 fishes and other enemies, and partly by the unfavourable cha- 

 racter of the water; while in the tubs the density of the water 

 is more favourable for their rapid increase, and uufavom'able 

 or fatal to their enemies*. The water from the tubs, when 

 examined with a high power of the microscope, was found to 

 be filled with immense numbers of Infusoria of various kinds, 

 such as Monads, Vibrios, and Bacteria, most of which w^ere so 

 small as to be distinguishable only as moving points with a 

 ^-inch objective. 



In the salterns of France the Artemiai are associated with 

 immense numbers of a monad, usually bright red in colour, 

 which has been named Monas Dunalii by Joly, who attributes 

 to it the red colour which the brine assumes just before crys- 

 tallization f, as also the red colour observed in the Artemia;^ 

 ^\■lliell doubtless feed upon it as Avell as upon various other 

 livimr Infusoria and dead animal and vetj;etable matter of va- 

 rious kinds |. The Monas DunaUi appears in abundance in 

 the water having the density most favourable for Artemia, but 

 increases in far greater ])roportion in the still denser, nearly or 

 quite saturated brine in which Artemia does not live. The 

 observations of Payen and Joly show that the A. saliiia of 

 France can exist in waters varying in density from 4° to 20° 

 Baumc, but that they flourish best in those that have a density 

 of 10° to 15° §. According to Kackett, those of Lymington 



* The density of the water in two of the tubs containing most Artetm'(K 

 was l-0(>5, equivalent to a brine coutainin-r 007 per cent, of salt. One of 

 those tested was brownish, the otlior milky. 



t '* Recherchcs sur la Coloration en llousre des Marais Salans M(5di- 

 terraneens," par M. Jolv (Ann. d. Sci. Nat. 1^40, sor. 2. t. xiii. p. 2(>G). 



X Accordin<r to >[. Joly (o/). o//. p. 2(52^ a beetle, Hi/droponui salinus, 

 Joly, abo inhabits the salterns where the water has a density of 6" or 7° 

 Baunit^, and preys upon the Artemia: 



§ 4° to 20° Baum^ is equivalent to a density of about 1-02 to 116: 



