42 ABIOLOGYOFCRUSTACEA 



haemoglobin is greater, and more haemoglobin is made. The effect 

 of an increase in temperature is accentuated by the fact that haemo- 

 globin has a lower affinity for oxygen at higher temperatures so that 

 when the temperature is increased more haemoglobin is necessary 

 to obtain the same amount of oxygen as was obtained at the lower 

 temperature. 



The effect of an increase in temperature, in increasing the 

 metabolic rate, is paralleled by individual variations in activity. 

 Males for instance are more active than females, they have a 

 higher rate of oxygen consumption, and they have a higher con- 

 centration of haemoglobin in their blood than females kept in the 

 same conditions. Similarly the small active Daphnia curvirostris 

 has a higher concentration of haemoglobin than the larger, more 

 sluggish D. magna, when both are in the same conditions. There 

 are even races within one species of Daphnia which differ in their 

 metabolic rates, and consequently differ in the concentration of 

 haemoglobin in their blood. A British race of Daphnia magna has 

 been found which makes more haemoglobin than a race of the 

 same species from the south of France. The British race also grew 

 faster and produced more eggs. 



Haemoglobin is also found in the eggs of Daphnia, where it serves 

 the function of enabling development to proceed in poorly aerated 

 water. Eggs which have been treated with carbon monoxide develop 

 more slowly than untreated eggs. 



The functional basis of haemoglobin synthesis in relation to 

 oxygen deficiency is easy to understand, but the reason why haemo- 

 globin should be lost when Daphnia enters well aerated water is not 

 at all clear. It is inevitable that the females should lose haemo- 

 globin, because they pass it into their eggs, and if the water is well 

 aerated they will not be stimulated to make more. When females 

 are producing a large number of eggs this passage of haemoglobin 

 into the eggs is sufficient to account for the usual rate of loss. How- 

 ever, males also lose haemoglobin and so do females which are 

 producing few or no eggs. The second way in which haemoglobin 

 is lost is by breakdown in the fat cells, which lie at the bases of 

 the limbs and alongside the gut. Under certain conditions globules 

 of haemoglobin can be seen in these cells. These globules eventually 

 disappear and the blood is left pale. The distribution of iron in the 

 tissues during haemoglobin breakdown also indicates the fat cells 

 as the site of breakdown, and, further, indicates that the freed iron 

 is excreted via the maxillary glands. 



