292 UNITY AND DIVERSITY IN BIOCHEMISTRY 



Rhodophyceae whilst c-phycoerythrin is present in the Myxophyceae. 

 Among the phycocyanins, r-phycocyanin is present in the Rhodophyceae 

 and c-phycocyanin in the Myxophyceae. The phycobiHns serve to absorb 

 light and transmit energy to other systems, notably the chlorophyll system. 



Plants are able to continue the synthesis of porphyrins along the "iron 

 branch" and along the "magnesium branch" whilst in animals the latter is 

 lacking. However, animals have particularly developed the "iron branch" 

 as far as the biosynthesis of the compound of haem and globin, haemo- 

 globin, is concerned. The biosynthesis of haemoglobin is sometimes 

 observed in plants, for example in the root nodules of Legumes. In animals, 

 the presence of haemoglobin in tissues other than blood has often been 

 demonstrated. For example, it has been shown to occur in the nervous 

 system of certain worms e.g. in the Annelid Aphrodita and in a number of 

 the Nemertea : Polia, Meckelia and Borlatia. 



In Insects haemoglobin is found in the Diptera and the Hemiptera. 

 In Gastrophilus intestinalis which, during its larval period, is a parasite in 

 the stomach of the horse, the young larva is a uniform red due to the 

 coloration, by haemoglobin, of the fatty bodies, of the parietal muscles and 

 of the hypodermis. As the larva grows further the haemoglobin becomes 

 localized in special cells, the tracheal cells, forming a red mass localized in 

 the posterior third of the body. 



In certain of the Hemiptera such as Buenoa margaritacea and Anisops 

 producta, the haemoglobin is similarly localized in masses made up of 

 tracheal cells. In addition in another Hemiptera, Macrocrixa geoffroyi, 

 haemoglobin is present in the accessory glands of the male genital system. 



Vertebrate muscle contains a haemoglobin known as myoglobin and the 

 respiratory pigment has also been demonstrated in the pharyngeal muscles 

 of a number of gastropod molluscs {Pahidina, Littorina, Limnaea, Patella, 

 Chiton, Aplysia) and also in the body wall of Ascaris lumbricoides. 



The presence of haemoglobin in the blood is a general characteristic of Ver- 

 tebrates: it is always contained in blood cells, either nucleated or non- 

 nucleated. Nevertheless, some fishes adapted to cold waters have been shown 

 to have no haemoglobin and no er)^hrocytes in their blood whatsoever. 



The distribution of haemoglobin in the blood of Invertebrates, where it may 

 be present either in cells or dissolved in the blood, defies all systematization. 



Among the Echinoderms, corpuscles containing haemoglobin have been 

 demonstrated in one, sometimes in two, and occasionally in all three of the 

 body fluids of the Ophiuroidea and in several of the Holothuroidea. 

 Corpuscles have never been found in the Asteroidea, the Echinoidea, nor in 

 those Holothuroidea that possess a test. 



The presence of a haemoglobin in the blood or coelomic fluid of annelid 

 worms has long been known. In the Polychetes there is generally a cir- 

 culatory system and a red blood containing dissolved haemoglobin 



