No. 398] WILLEY ON THE ENTEROPNEUSTA. 127 
is the fact that in certain adult individuals of one species of 
Ptychodera he finds sometimes one, sometimes the other, of the 
two proboscis pores opening “into the base of the medullary 
tube somewhat behind the anterior neuropore." In younger 
specimens he finds the single median proboscis pore opening 
somewhat in front of the “anterior neuropore.” The occasional 
peculiarity he has observed in Ptychodera carnosa seems a rather 
narrow apex on which to found so broad a pyramid of theory. 
Willey's third proposition as to regional pores and neph- 
ric tubules is best presented by copying his own table, which is 
self-interpreting, with the one explanation that the organs men- 
tioned in the right-hand column are not intended to be repre- 
sented as serially homologous with those in the preceding 
columns. 
Group A S EssENTIAL ORGANS 
* RCHIMERIC SYSTEM. or EXCRETION 
Ideal Pos : Mesomeric Opisthomeric | Regional pore 
. + » |E IOLVOIIICIIC pores pores pores canals 
Entero- Truncal pores 
i 1 1 
pneusta Eosigecn e (Spengelia) — 
Cephalo- Przoral pit Hatschek's Lankester’s | Boveri’s nephric 
chorda jand Olfactory pit) nephridium | brown funnels tubules 
Renal vesicles: 
Urochorda Neuro-hypophy- | Organ of Bo- 
sis (in part)! janus(Molgu- 
lidze) 
A Pronephros 
Vertebrata dh Mesonephros 
Un en Metanephros 
In some of the Ptychoderidae Willey found that the collar 
nerve tube does not completely separate from the dorsal epider- 
mis from which it arose, but that there are partially hollow con- 
necting strands running from the nerve tube to the mid-dorsal 
line of the collar, The more or less interrupted lumina of these 
1 In part because coelomic element is wanting. 
