588 General Notes. - [June 
no direct evidence. It is more probable that the nephridia are 
of mesoblastic origin, as in other vertebrates. 
“Van Wijhe finds that in the ray the pronephros ( Vorneire) 
arises at the commencement of Balfour’s stage I., as a continu- 
ous evagination from the somatopleure on each side of the body 
throughout five somites. When the hinder end of this evagina- 
tion reaches the skin it fuses therewith, and the place of fusion 
is the rudiment of the duct of the pronephros (segmental duct). 
This grows posteriorly, gradually separating from the skin, so 
that its latest-formed end is always fused with it. The meso- 
nephros (Urniere) is developed shortly after the appearance of 
the pronephros. 
“In the frog Perényi finds that the duct develops as a canal- 
like separation from the inner (nervous) cell-layer of the epiblast, 
which later associates itself with the mesoderm cells of the inter- 
mediate cell-mass (Grenzstrang). 
“According. to the usually-received account, formation of the 
segmental duct may take place in two ways,—(r1) either by the 
‘closing in of a continuous groove of the somatic peritoneal epi- 
thelium (Cyclostomi, anterior end only; Lepidosteus, Teleostei, 
Amphibia); or as a solid knob or rod of cells derived from the 
somatic mesoblast, which grows backwards between the epiblast 
and the mesoblast (Cyclostomi, posterior portion; Elasmo- 
branchii, Amniota).” 
giving especial prominence to the views of Balfour on this dif- 
ficult problem as discussed in his “ Comparative Embryology,” 
vol. ii. He then refers at length to the view propounded by 
: entation,” and cites , who says, “In certain 
Polyclades [Turbellaria] ramifications of the intestine open to 
the exterior by excretory pores, either on the dorsal surface 
(Planaria aurantiaca d. Ch.), or on the lateral edge (as in a very 
interesting new genus of the family of Proceridz), thus forming 
_ acomplete analogy with the excretory pores which are found at 
the edge of the bell in certain Medusæ. 
“ The aquiferous system characteristic of other Platy-elminthes 
does not occur in the Polyclades. The secretory organs of these 
animals are formed after the type of those of the Ccelenterata. 
‘Excretion in the two groups is ae pete by means of diver- 
ticula from the intestine which open fo the exterior.” 
__ Van Wijhe’s view is briefly summarized to the effect that the 
primitive Craniota had no pronephric duct, the pronephros open- 
ing outwards by a pore from the gland. Later, this orifice mi- 
grated backward and its outer border developed into the duct, 
and, approaching the cloaca, blended with and opened into it. 
_ He also thinks that the epiblastic origin of the segmental duct 
will not be welcome to those who think that the Chordata were 
