LESSKU LING. 



525 



This opinion is untenable, for the two species are di- 

 stinguished by constant characters; but the manner in 

 wliich most of these characters develop in Molua dip- 

 tei'i/fjin, as far as we can decide from an examination 

 of four adult specimens and without any knowledge 

 of the earlier stages, shows that, from a systematic 

 and genetic point of view, Molua dipteryrjla must be 



regarded essentially as a predecessor of the common 

 Ling, though the former has evidently adopted in cer- 

 tain respects a distinct direction of development fi'om 

 the common original type which we are entitled to 

 assume. This appears from the following talde of 

 averages; which may besides serve to supplement the 

 preceding description. 



A V e r a 1? e s. 



Molua dipterygia". 



spccimeDB. 



2 

 spc'ciinens. 



Molua molva''. 



specimens. 



specimens. 



Length 111' the body esprcssed in millimetres _. 



,, ., .. bfise of the fir.st dor.sal fin , in % of the length of the hodv 



Distiince helwceu the second dorsal Hu and the tip of the snout „ ,, ,, „ ,, „ ,, ., 



,, insertion of the ventral tins and the l)egiuning of the anal tin 

 ., ,. ., tip of the snout ,, ,, ,, ,, ,, „ ,, 



Length of the base of the aniil fin _ 



,, ,. .. head in % of the length of the base of the anal tin 



Longitudinal diameter of the eyes in % of the length of the snout 



7, ,. ;» ,, 



ij ?T )» J» 



Breadth of the interorbital spaee in '/« of the distance between the tip of the snout and the tjind extremity of 

 the mamillaries _ ._ 



Postorbital length of the head in % of the length of the base of the second dorsal tin _ 



Distance between the second dorsal tin and the tip of the snout iu % of the length of the liase of this tin 



Length of the pectoral tins in fo of the distance between the insertion of the ventral tins and the beginning of 

 the anal fin _. .__ _ 



Height of the first dorsal fiu in °» of the length of its base _ _ 



Length of the snout in % of the length of the body _ 



„ „ ., base of the second dorsal fin ,, „ ,, „ „ ,, ,, ,, 



Length of the snout in % of the length of the pectoral fins 



Least depth of the peduncle of the tail in % of the length of the middle caudal rays - 



Height of the first dorsal fin in % of the length of the body 



Least depth of the peduncle of the tail in % of the length of the body ._ 



,, ., ,, ,, ., ., .. ,, ,, ,, ., ,, „ ,, ., head 



Distance between the tip of the snout and the hind extremity of the maxillary bones in J^ of the length of the head 



7.1 

 33.2 

 24.2 

 41.. 5 

 4G..5 

 40.3 



71). 2 



24.0 

 l(j.5 

 63.5 



42.7 

 102.9 



.").8 



52. G 

 56. 7 



42.2 

 7.2 



2 7 

 14.2 



46. 3 



IS24 

 8.1 

 33.5 

 25.3 



41.7 



45.1 

 42.0 

 67.7 



26.0 

 16.9 

 65.3 



41.8 



101.4 



6.2 



51.3 



59.0 



39.H 



8.1 



2.5 

 13.4 



46.7 



319 



10.6 



39.3 

 27.7 

 46.7 

 38.1 

 56.6 



61.9 



32.3 

 23.2 



86.4 



33.1 

 48.7 

 7.0 

 45.5 

 76.4 



71.5 

 5.2 

 4.8 



22.3 



42.7 



892 

 11.6 

 40.0 

 29.5 

 48.9 

 37.9 

 56.8 

 47.3 



39.1 

 25.2 



87.6 



31.6 



48.9 



6.8 



45.9 

 73.8 



78.3 



5.7 



4.6 



21.7 



43.8 



In the first 11 points of the comparison drawn 

 in this table the averages run in the same direction, 

 from a. lower percentage to a higher or vice versa, and 

 thus form an uninterrupted developmental series, the 

 direction of development being the same in both species. 

 In the next five points (12 — 16) the directions of de- 

 velopment are different, Jloliia dipterygia seeming in 



these respects to have followed a distinct course'" and 

 to have had a special origin for its development. In 

 the last four points (1 7 — 20) the direction of develop- 

 ment is again the same, but at the origin of its course 

 of development Molua dipterygia seems to be already 

 further advanced than Molua molva. 



MiriimiHii length of tlie body in these 4 specimens 562 



1 2=!1 



iiia.xiniiini 828 iiiin. 

 1,640 „ 



' The difference is to be exi:)lained to some extent, liowever, in points 13 and 14, by the fact that one of the specimens of Molua 

 iiiolca is 1,640 mm. long, and in several respects is an example of the not unusual circumstance that old age involves a reversion to the 

 characters of yoiitli. 



