304 A. T. MASTERMAN. 



and altered in outline. I have found no indication that the 

 fusion of the vacuoles with each other takes place. The position 

 of the organs in situ is seen in PI. 18, fig. 1, and PI. 21, 

 fig. 38 {nch.), in lateral view, whilst fig. 3 gives the dorsal 

 view of the two notochords (nch.). In PI. 20, fig. 22, their 

 appearance in coronal section can be followed, whilst fig. 19 

 shows a sagittal section of one of them. 



We may emphasise the fact that development of the noto- 

 chords proceeds in two ways : — 1. The organs themselves arise 

 from a pair of evaginations of the antero-lateral walls of the 

 pharynx, which gradually become longer and deeper till they 

 extend forward in close contiguity with the mesentery between 

 the collar and the pre-oral lobe. They have no connection 

 whatever with the epiblast. 2. At the same time as this 

 growth in length the cells undergo a remarkable metamor- 

 phosis into vacuolated tissue. 



These organs will be compared to the notochord of the 

 higher Chord at a. As regards previous observations upon 

 them, we may say at once that the majority of the numerous 

 workers on Actinotrocha were quite content to describe 

 them as " liver diverticula." 



Thus Wagener (20) refers to the " liver-blind-diirme/^ and 

 Gegenbaur (9) as heaps of cells (liver-cells ?) : Caldwell (2) 

 remarks, '' The stomach at its anterior end is produced into 

 one or two ventral processes. In the vacuolated walls of 

 these structures brown concretions are present " (p. 378). 

 Claparede (5) described it as a dark mass with light balls 

 embedded in it, no doubt in allusion to the appearance in the 

 live animal, in which the dark areas are formed in the same 

 way as the black rim of an air-bubble under the microscope. 

 Schneider (18) accepts Claparede's interpretation, and gives 

 up his former view that they were fat- globules, but does not 

 clear up the point any further; he remarks that the " balls" 

 are surrounded in Actinotrocha with black pigment, in 

 allusion no doubt to the refractive effects above mentioned. 



Metschnikoff' (14) gives a figure (fig. 6) of a larva with four 

 pairs of arms, in which the vacuolisation of the antero-lateral 



