240 PHYSIOLOGY OF THE INVERTEBRATA. 



Drs. MacMunn and Krukenberg have extracted several, 

 lipocliromes from these animals. 



In concluding our account of the function of respiration in 

 the Invertebrata, we may summarise the contents of this' 

 chapter in the following manner: — (i) There is respiration 

 by the general surface of the body. (2) Respiration by 

 air dissolved in water. In this mode of respiration the 

 respiratory organs are either internal (contractile vacuoles, 

 water-vascular systems, pseudo-haemal vessels), or external 

 (gills). (3) Respiration of air directly; this mode being 

 performed by three distinct mechanisms, of which the first 

 is the respiration of air (not dissolved in water) by the 

 general surface — i.e.,- cutaneous respiration. The second is 

 by means of the tracheae or air-tubes ; and the third by 

 pulmonary sacs or rudimentary lungs.* 



In addition to the above modes of respiration there is also 

 tissue-respiration by means of various pigments. These 

 pigments are capable of retaining oxygen within the system, 

 and no doubt they play a most important part in the respira- 

 tion of the Invertebrata; and possibly they play a more 

 important part in these animals than in the Vertebratd, where 

 the respiratory apparatus becomes highly differentiated into 

 powerful and special organs. 



* Gills first appear in the Polyahaita, tracheal tubes in the Myriapoda, 

 and a rudimentary ",lung " first makes its appearance in the Pulmogastero- 

 poda. 



