Fig. 18 From a specimen (444, 4-4-6) of the early swimming stage; fixation, 

 sublimate acetic; staining, Boomer's hematoxylin and orange G in 60 per cent 

 alcohol slightly acidulated with hydrochloric acid; sections, 10 m, transverse. 



Fig. 19 From the same specimen (444, 2-2-5) as the last. 



Fig. 20 From a specimen (570, 2-2-5) of the early swimming stage; fixation, 

 Zenker's fluid; staining, iron hematoxylin; sections, 1 fx, in the frontal plane. 



Fig. 21 From a specimen (412, 5-1-3) of the early swimming stage; fixation 

 and impregnation according to Eaton's modification of the nitrate of silver 

 method; sections, 6 f/x, in the frontal plane. 



Figs. 22 to 23 From the same specimen (412, 5-2-3) as the last. 



Fig. 24 From a specimen (408, 4-3-9) of the early swimming stage; method and 

 sectioning the same as the last. 



Figs. 25 to 26 From the same specimen (408, 4-3-10) as the last. 



Fig. 27 From the same specimen (408, 4-3-11) as the last. 



Fig. 28 From the same specimen (408, 3-2-7) as the last. 



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