ANIMAL CHLOROPHYLL 343 



are the most significant examples — which favours Lankester's 

 hypothesis of the intrinsic nature of certain of the animal 

 chlorophylls. Nevertheless the balance of evidence seems to 

 favour the algal theory to account for chlorophyll in animals ; 

 and it is probable, moreover, that further investigation with 

 a more refined technique will show conclusively that Lankester 

 was wrong. Particularly does this seem probable in the light of 

 the classic researches of Gamble and Keeble (which will be dis- 

 cussed later) on Convoluta, the green cells of which were shown 

 to be intruding algae. In short, the Protozoa do not present any 

 real difficulty to assuming that body-pigments arise in the blood. 



The sponges possess nothing in the nature of a blood-system : 

 nutrition and respiration being accomplished by water currents 

 within the body. What, then, is the nature of their coloration '? 

 Is it an animal pigment, which has arisen independently of the 

 blood-system ; or is it, as in the Protozoa, a chlorophyllous 

 substance ? Though it has not been demonstrated that every 

 species of sponge contains chlorophyll, the spectroscopic 

 investigations of Borby (1875 a), Krukenberg (1884), and 

 MacMunn (1888) have estabhshed the presence of a chloro- 

 phyllous pigment in eighteen species of sponge, it being most 

 common in the genera Halichondria and Halina. The more 

 highly-coloured sponges possess pigments the absorption bands 

 of which (as indicated by the figures of MacMunn and Kruken- 

 berg) resemble in many respects those of certain of the pigments 

 from blue and red algae, the pigment spectra of these sponges 

 is, in addition, quite different from the spectra of chlorophyll. 

 Inasmuch as it has been shown that the presence of small 

 quantities of such algal pigments as phycocyanin, phycophaein, 

 and phycoerythrin (Phillips, 1911 ; also Willstiitter and Stoll, 

 1913) greatly alter the spectrum of chlorophyll, the fact that 

 the pigment of certain coloured sponges fails to show the bands 

 characteristic of the plant pigment does not necessarily indicate 

 its absence. As in the Protozoa, one is also confronted in the 

 Porifera with a question concerning the nature of the pigment 

 itself — a point which is as yet unsettled. Lankester (1882) 

 and his school were vigorous in upholding the animal origin 



NO. 262 B b 



