DEVELOPMENT OF ACANTHODRILUS MULTIPORUS. 521 
genital funnels in the earlier stage were really metamorphosed 
into the proximal part of the genital duct; at any rate, there 
was no trace in the young worm of these solid rods, except in 
the segments in front of and behind the genital segments, other 
than the straight genital duct. 
The temporary occlusion of the lumen during the develop- 
ment of the vasa deferentia and oviducts marks the change in 
their function from excretory tube to efferent ducts of the 
genital products. Itis, however, also shown that the nephridial 
tubes are destined to undergo this physiological change, 
though in a less degree; in a less degree because the funnel, 
which possesses an obvious lumen in the youngest stages 
(Pl. XXXI, fig. 18), never seems to recur to this condition, any 
more than does the immediately following section of the tubule. 
It has appeared to me, however, that in the adult worm part 
of the nephridia had regained the lumen temporarily oblite- 
rated. In any case the occlusion and reopening of the lumen 
does occur with the genital ducts. This phenomenon seems to 
be connected with the growth of the tubes; although remark- 
able, it is not without parallel. Balfour (8) discovered that 
in Elasmobranchs the cesophagus during development became 
solid, and then reacquired a lumen. ‘The solidification of 
the csophagus,” he remarks (8, p. 218), ‘‘ belongs to a 
class of facts which are curious rather than interesting, and 
are mainly worth recording from the possibility of their turn- 
ing out to have some unsuspected morphological bearings.” 
More recently (16) Dr. Milnes-Marshall and Mr. Bles have 
observed precisely the same phenomenon in the developing 
frog. The solid esophagus is “a constant feature in tadpoles 
of from 74 mm. to about 10} mm. in length.” 
These observers have not referred to a paper by de Meuron 
(14), in which a similar temporary closure of the esophagus 
is described in the chick.! 
1 T am indebted for this reference to Professor Howes. 
VOL, XXXIII, PART IV.—NEW SER. NWN 
