^'I'gi^' ] Cleland and JOHNSTON, Red Blood Cells. i8g 



Before discussing their significance it may be well, first of all, 

 to briefly indicate the results of our examinations. It may be 

 stated here that all the measurements are in micromillimetres. 

 The largest red cells we have met with are those of Ceratodus 

 forsteri (39 x 23 to 25). These, in size, link in on the one hand 

 to the Elasmobranch fishes, amongst which Chiloscyllium has red 

 cells of 23 X 13.5, whilst in Dasybates kuhli and the hammerhead 

 shark {Sphyrna tiides) the red cells only reach 18 x 12.5 to 14.5. 

 The Teleostean fishes have red cells very much smaller, varying 

 from 6 to 7 (almost round) to g x 7 and 10 or 12.5 x 9. On the 

 other hand, Ceratodus links on with the Batrachians, where the 

 size is generally from 18 to 19.5 x 12.5 to 14, and with the 

 reptiles, amongst which Chelonians have cells of 17 to 21 x 12.5 

 to 14.5, snakes 17 to 20.5 x 9.5 to 12.5, and lizards usually 15 to 

 17.5 x 7 to II. Amongst birds, we find the largest red cells in 

 the Ardeiformes (13 to 16 x 8 to 9) ; then come the Charadrii- 

 formes, usually 13 to 14.5, occasionally 15, x 7 to 8 ; the Galli- 

 formes, up to 14 x 7 to 8, &c. : whilst the smallest are the Passerines 

 (9 to 12.5 X 6 to 7). 



Fishes. 



Amongst the fishes, the Dipnoi, or lung-fishes, have cells of 

 monstrous size, being, next to those of some amphibians, we 

 believe, the largest known. In Ceratodus they measure 39 x 

 23 to 25, whilst in Proteus they are given * as 58 x 35, and in 

 Amphiuma as 77 x 46. Of the three Elasmobranchs examined, 

 we find an interesting and important difference. Chiloscyllium 

 has cells 23 x 13.5. whilst Sphyrna Hides and Dasybates kuhlii have 

 cells of only 18 x 12.5 to 14. The cells of Teleostean fishes are 

 much smaller and usually rounder, sometimes almost spherical. 

 There seems to be a good deal of variation, from 6 to 7 (about 

 the usual size of mammalian red cells) to 12 or 13. Future se- 

 search may show whether any groupings, indicating degrees of 

 remoteness from Elasmobranchs, may be found in the various 

 orders or families. 



These results are of great interest. They show that under the 

 one general term "fishes" are grouped vertebrates with red cor- 

 puscles varying as greatly as do those of amphibians or reptiles 

 from those of birds. 



Another interesting point is that in one of the oldest vertebrate 

 groups known, the Elasmobranch fishes, the red cells are of large 

 size, and that we have found that amongst these again in one 

 (Chiloscyllium) they are much larger than in the other two 

 examined, and this genus seems hence intermediate between 

 these two and Ceratodus. Ceratodus, from its red cells, links on 

 to certain of the Amphibians. These results suggest, perhaps, 

 two separate lines of evolution from the smaller-celled Elasmo- 

 branchs — one with Chiloscyllium and then Ceratodus as offshoots 

 from a stem with red cells of increasing size, which eventuallj' 



* Schafer, " Essentials of Histology " (6th ed.), p. 37. 



