1887] Embryology. 589 
descended from Annelids; but, a his part, he cannot admit the 
relationship between these t 
rofessor Haddon then des his own view, as follows: 
“Without at all committing myself to a belief in the ancestry 
now that the epiblastic origin of the segmental duct has been 
established. 
“It is perfectly well known that the nephridia of all inverte- 
brates open directly to the exterior, and in the ance worms 
there are typically a pair of nep ridia for each s 
“It is generally admitted that the early (not m the 
primitive) Chordata were segmented, and it is not unreasonable 
tubules in ontology. The peripheral orifices of the nephridia 
must either have opened directly to the exterior or from the first 
debouched into a longitudinal canal. Various theories have been 
framed to explain the latter arrangement, but the former con- 
dition is undoubtedly more easily conceived, one difficulty in 
this supposition pees —What has become of the primitive 
external openings ? 
“ Accepting the proposition that in the primitive Chordata 
nephridia opened directly to the exterior, we have only to as- 
sume that the lateral area along which they opened was grooved, 
and that this groove extended posteriorly as far as the anus. 
“From the analogy of the neural groove there is no great dif- 
ficulty in further supposing that the nephric groove was converted 
_ into a canal, which, becoming separated from the overlying epi- 
blast, might sink into the deeper-lying parts of the body. 
suggestion may be hazarded concerning the advantage 
of Savatie the nephric groove into the nephric duct, it may 
be pointed out that the lateral openings of the nephridia would 
pure water for respiratory purposes is emphasized by the now 
acknowledged fact that each cleft was provided with its own 
sense-organ (now metamorphosed into the ‘thymus gland’). 
The development of the duct from before backward supports 
this vi Sako 
“From recent researches on the lamprey (Shipley), newt 
(Alice Jolson), Alytes (Gasser), and frog (Spencer), it has been 
proved that in these forms the blastopore never closes up, but 
persists as the anus (ż.e., the opening of the mesenteron into the 
oaca). 
“We are justified in assuming the persistence of the blasto- 
pore as the anus in early Chordata; thus, if the nephric groove 
were continued round to the anus it would practically open into 
