WOLFFIAN DUCT AND BODY IN THE CHICK, 455 
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 1s one primary tubule in a segment, 
in Spelerpes fuscus there are two. 
Further, Firbringer 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 friheren Entwickelungsstadien 
leicht zu scheiden ; spiiter 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 thie 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 Ceecilia, in which the anus is almost 
terminal, very few segments being placed behind (tail undiffer- 
entiated), we find that the kidney is segmental, 7. 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 Lacertilia® 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 chick* the 
number of primary tubules in a segment increases with the age 
of the embryo. 
These three facts, viz.—(1) 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. 
3 Braun. 
4 Self, ‘ Quart. Journ. Mier. Sci.,’ April, 1880. 
5 There is no evidence that this is effected by intercalation in the chick 
at any rate. 
