144 ARTHQE WILLEY. 



taken place ; and the consequence is that they do not at first 

 occur one behind the other in the longitudinal direction along 

 lines parallel to the longitudinal axis of the larva, but they 

 lie somewhat obliquely in a subvertical or dorso-ventral 

 direction, one being dorsad of the other, i, e. one of them is 

 nearer the oral or dorsal side of the body, Avhile the other is 

 nearer the ventral side (cf . my PI. 30, fig. 2, op. cit.) . 



The figures 1 to 5 on pi. xxi of M. Julin's memoir (op. cit.) 

 represent transverse sections through a tailed larva of Ciona 

 intestinalis, preserved fifteen hours after hatching. This 

 larva is described as possessing one pair only of primary 

 branchial stigmata, in the form of a nearly transverse bran- 

 chial tube on each side, opening by an internal aperture 

 into the pharynx and by an external orifice to the exterior. 

 This branchial tube is regarded by M. Julin as the primor- 

 dium of the corresponding half of the peribranchial chamber. 



In M. Julin's fig. 1 the right branchial tube is seen to open 

 internally at the extreme dorso-lateral angle of the pharynx, 

 whereas in fig. 2, which we are told represents the next 

 section in the series, it passes through the external (atrial) 

 orifice of the right side, and the same branchial tube opens 

 internally through the middle of the wall of the pharynx 

 i. e. at quite a different (lower) level. I cannot understand 

 how the right internal orifice of the branchial tube shown in 

 M. Julin's fig. 2 can be identical with the right internal orifice 

 of fig. 1. Remembering the primary axial relations of the 

 two first-formed stigmata, and their slightly oblique position, 

 one being below and somewhat behind the other, I should 

 rather interpret M. Julin's figs. 1 and 2 as passing respectively 

 through the two branchial stigmata of the right side, these 

 stigmata in their turn communicating with the exterior by 

 way of the right atrial chamber. 



It will soon be evident that the two first-formed stigmata 

 have identical properties and identical fates, thereby creating 

 a strong presumption in favour of the identity of their origin. 



The distigmatic stage of Phallusia mammillata was 

 described by Krohn (' Miiller's Archiv,' 1852), who also ad- 



