Blood of Larva 77 



becomes aerated in them ; the return-current during 

 diastole passes by the ostia into the heart again. 



The red colour of the larvae of some species of Chiro- Biood <.f 

 nomus has long been familiar. It must be due to some- 

 thing contained in the blood, for when a larva is cut open 

 and gently squeezed, the body- wall and alimentary canal 

 become pale, while the escaping fluid, if collected in fair 

 quantity, for which a number of larvae must be sacrificed, 

 is of a lively red. The colouring matter is dissolved in 

 the fluid or plasma of the blood, and is not restricted to 

 the corpuscles, as in vertebrates. A point of special 

 interest is that the colouring matter is haemoglobin, the 

 same substance which gives a red colour to the blood of 

 man and other vertebrates. This was first shown by 

 Eollett (1861). He collected the blood of Chironomus- 

 larvae in quantity, and obtained from it crystals of 

 haemoglobin ; he also showed that it is dichroic, the light 

 which lias traversed a sufficiently thick stratum being- 

 red, while tliat which has jDassed through a very thin 

 layer is green \ Briicke had shortly before (1853) shown 

 that the venous blood of the frog is also dichroic. In 1867 

 Lankester ^ showed that the blood of Chironomus-larvae 

 gives the characteristic absorption-spectrum of haemo- 

 globin. It is a striking fact that haemoglobin should occur 

 in a number of animals which are not closely related to 

 one another. This peculiar respiratory pigment occurs in 

 very nearl^^ all vertebrates, as well as in the following 

 invertebrates : — a small planarian, found at Suez by the 

 late H. N. Moseley, some nemertines (where it is often 

 specially associated with the nervous system, but may be 

 found in red corpuscles), some leeches, many chaetopod 



' Attention to this dicliroic property of the blood is necessary to avoid 

 drawing wrong conclusions fi"om the colours seen in the different tissues 

 of Chironomus-larvae. 



^ Journ. Anat. and Phys., ii, p. 114 (1867). 



