36 ADAM SEDGWICK. 



Spengel has also shown that even in different species of one 

 genus the number of primary tubules in a segment differs, e.g. 

 in Spelerpes variegatus there is one primary tubule in a segment, 

 in Spelerpes fuseus there are two. 



Further, Fiirbringer states that in the species investigated by 

 him the number of primary tubules in a segment increases with 

 the age of the animal. 



" Die Anlagen sind in ihren friiheren Entwickelungsstadien 

 leicht zu scheiden ; spater hingegen lagern sie sich so innig an 

 einander, dass eine Abgrenzung unmoglich wird.''^^ 



Finally, there seems to be a distinct relation between the 

 closeness of aggregation of the tubules with regard to the body 

 segments and the number of segments found between the 

 mouth and the anus. 



In the Anourous Amphibia, where there are very few segments 

 in the adult in this region, we find a very compact and complex 

 kidney. 



In the Urodeles, in which the number of segments is greater, 

 the kidney occupies a greater number of segments, and is not 

 nearly so compact, while in Ccecilia, in which the anus is almost 

 terminal, very few segments being placed behind (tail undiffer- 

 entiated), we find that the kidney is segmental, i. e, one primary 

 tubule is found for each segment, and it occupies in the adult 

 as many as sixty segments.^ 



Turning to the Amniota, we find that in Lacertiha ^ the 

 mesonephros has at first a segmental arrangement, one primary 

 tubule for each segment, and although it has not been shown that 

 the fully developed mesonephros of lizards has lost this feature, 

 still there can be little doubt, considering its resemblance to that 

 of Aves, that it has; while in the case of the cbick* the 

 number of primary tubules in a segment increases with the age 

 of the embrjo. 



These three facts, viz. — (I) The variability of the number of 

 primary tubules in a segment in closely allied forms, (2) the 

 increased ^ number in a segment as development proceeds, (3) the 

 relation between the compactness of the kidney and the number 

 of segments over which it extends, all point in the same direc- 

 tion. They seem to indicate that the tubules of the Wolffian 



segmental tubules in each segment over its whole area ; while in the male, 

 he finds that they increase in number behind. 



1 Loc. cit., p. 19. 



2 Spengel. 

 ' Braun. 



< Self, ' Quart. Journ, Micr. Sci.,' April, 1880. 



* There is no evidence that this is effected by intercalation in the chick 

 at any rate. 



