PHYSIOLOGY OF THE INVERTEBRATA. 129 



The Annelida. 



The perivisceral cavity, communicating with the excretory 

 or segmental organs, contains a corpusculated fluid which is 

 nutritive. The corpuscles are oval, flat, granular, colourless 

 bodies without a limiting membrane. Besides these corpuscles, 

 the blood of the Annelida contains " actual cell corpuscles of 

 fusiform shape, and devoid of granules. Here, then, are 

 some corpuscles with a true wall, but all the solid, floating 

 particles of the blood are not yet of that high order of 

 structure." 



The fluid present in the pseudo-hajmal system or vessels 

 of the Annelida contains a substance allied to haemoglobin ; 

 and according to Dr.MacMunn, this red colouring matter func- 

 tionates in a similar manner to the histohsematins of other 

 Invertebrates, i.e., it has a respiratory function. It will be 

 noticed, that there is in the case of the pseudo-heemal system 

 of the Annelida a fusion of the functions of circulation and 

 respiration. This hemoglobin is dissolved in the fluid and 

 does not belong to the corpuscles. It is questionable whether 

 this " respiratory blood," as Prof. Huxley* calls it, possesses 

 any nutritive properties ; it appears to be entirely devoted 

 to the function of respiration. 



In the Gephyrea, represented by Sipunculus, the blood 

 corpuscles contain a coloured fluid between the external wall 

 and the central nucleus. This is the first appearance of a 

 coloured corpuscle, but it differs essentially from the coloured 

 corpuscles of the Mammalia, for in the latter the colouring 

 matter is distributed throughoiit the corpuscle. 



Prof. E. Ray Lankester, F.R.S.,t has shown that the 

 perivisceral cavity of Sipunculus nudus contains a pale 

 madder-like colouring matter, " which is due to a large 

 number of coloured corpuscles from ^sVo to joVtt of ^^ 



* The Anatomy of the Invertebraied Animals, p. 57. 

 f Proceedings of Roxjal Society, vol. 21, p. 71. 



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