398 



PHYSIOLOGY AND MORPHOLOGY OF ANIMALS. 



all invertebrates there are blood-sinuses or reservoirs 

 in various parts of the body, into which the blood is 

 discharged, and from which it is again taken up. 



(3) In vertebrates the oxidized blood is bright red 

 and the deoxidized blood dark purple-red, and this, 



therefore, is the conven- 

 tional mode of repre- 

 senting these two kinds 

 of blood in colored dia- 

 gram. In default of col- 

 or we have used unshad- 

 ed and shaded spaces to 

 represent the same. We 

 continue to use the same 

 purely conventionally, 

 although in the case of 

 invertebrates there is no 

 such marked change in 

 color or shade. 



(4) The diversity 

 among invertebrates is 

 so extreme that it is im- 

 possible to do more than 

 select a few striking ex- 

 amples from each de- 

 partment. 



(5) In this selection 

 we pass over insects for 

 the present to come back 

 to them. The reason is 



the same which induced us to do so in giving the com- 

 parative morphology of the eye (page 162)— viz., that in 

 respiration and circulation insects are entirely peculiar, 

 and are outside of the direct line of evolution, or of 

 increasing complication as we go up. 



Fig. 276. — Lobster with the carapace 

 taken off : st, stomach ; dotted tube, 

 ii, intestines; L, liver; H, heart; 

 G } gills ; GG, green gland. 



