EXPLANATION OF PLATE HI. 



Fig. 1. Tail of the embryo of Sahno salar, with two hypural chondiifications in pro- 

 cess of fonnation, on the first day after hatching. Circa x 30. Slightly 

 modified from Lotz. 



Fig. 2. Tail of a somewhat older embryo of the same, with six hypural chondrifica- 

 tions in the process of formation, with embryonic rays at r uncovered at 

 the edge of the caudal fold, on the sixth to seventh day. From the same. 

 x30. 



Fig. 3. Tail of a still older salmon embrj-o, with seven hypural and two epural chon- 

 drifications being developed, and with the caudal rays more developed and 

 approaching the hypural elements, on the tenth to twelfth day. From 

 the same, x 30. 



Fig. 3a. Magnified view of one of the joints of an ossified fin- ray from a young sal- 

 mon. X 300. After Lotz. 



Fig. 4. Tail of a more advanced embryo, showing the principal caudal rays segmented 

 and in contact proximally with the free end of the hypural pieces, of which 

 there are ten, two of them having coalesced, while there are five epural 

 pieces represented by cartilaginous aggregations, two of which are in con- 

 tact with the chorda, and three in the position of " false spines," the last 

 two being rudiments around which the Deck-knocnen ossify, on about the 

 twenty-fourth day. x 30. From the same. 

 n, caudal notch dividing secondary caudal lobe from the tip of the primor- 

 dial larval tail ; Trts, medulla spinalis ; /(//, hypural pieces; ep, epural pieces : 

 r, rays; ch, chorda; cs, chorda sheath ; my, myotomes =: muscular somites 

 <[proto-vertebraB. (For the details of the development of the rays see 

 Plates IX and X.) 



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