592 THE ANIMAL KINGDOM. 



to the other points Bateson mentions, it may be noted, relative to the notochord of 

 BalanoglossuS) (i) that it is below, i.e. ventral, to the main dorsal blood-vessel, 

 whereas in all Chordata it is above, i.e. dorsal, to it; (2) that the histological 

 changes undergone by its cells may be simply correlated with its function as a sup- 

 porting structure, and indeed Spengel states that in the species examined by him, 

 the cells retain their cylindrical form and cilia, and that the organ is regenerated 

 with the proboscis after amputation. In the nervous system the presence of the 

 diffused sub-epidermic network of nerve fibres, of a peripharyngeal band and 

 ventral cord, are points of unlikeness to which attention should be paid ; and, it 

 may be added, the canals occurring in the dorsal cord, can scarcely be paralleled 

 with the neural canal of typical Chordata 1 . Nor can much weight be laid on the 

 absence of organs of special sense, or of specialised excretory organs. They are 

 features which are as likely as not due to the mode of life of the animal. 



Tornaria requires a fresh examination. The anterior enterocoelic pouch is 

 represented in it by a diverticulum, which opens on the dorsal surface, and is 

 eventually shut off from the archenteron, and its cavity is said to become the cavity 

 of the proboscis. The latter represents an overgrown praeoral or prostomial lobe, 

 and it has at its apex two eye-spots, resting on an epiblastic thickening, which 

 should by rights be the supra-oesophageal thickening (Balfour), but it seems to dis- 

 appear without leaving a trace. Balfour regarded Tornaria as intermediate in struc- 

 ture between the Echinoderm larva and the Trochosphere, resembling the former in 

 shape, in the longitudinal band of cilia, the origin and structure of the water-vascular 

 vesicle (= anterior enterocoelic pouch), and in the formation of the body-walls from 

 archenteric diverticula ; whilst Trochospheral characters are seen in the prostomial 

 eye-spots, the contractile band from the eye-spots to the oesophagus, the two 

 posterior ciliated rings, and terminal anus. It may be questioned which is the 

 more primitive form, Tornaria or Bateson's larva. In one feature the latter 

 appears to differ very markedly from Tornaria^ viz. in the dorsal anus, which 

 becomes terminal by the atrophy of the post-anal portion of the tail. 



Bateson, Q. J. M. xxiv. 1884; ibid. xxv. Suppl. 1885; ibid. xxvi. 1886. 

 Spengel, Mitth. Zool. Stat. Naples, v. 1884. 



Tornaria^ Spengel, Tagebl. d. Natf. Versaml., Mtinchen, 1877 ; Agassiz, Mem. 

 American Acad. of Arts and Sciences, ix. 1873 (or analysis by Perrier, A. Z. Expt. ii. 



1873)- 



Spengel is stated to be preparing a monograph of the genus in the c Fauna and 

 Flora of the Gulf of Naples,' New species have been recently described by Marion, 

 C. R. 101, 1885, and by Koehler, C. R. 102, 1886. 



For relations to Chordata^ see Bateson, op. cit. supra, and Id. ' The Ancestry 

 of the Chordata,' Q. J. M. xxvi. 1886; cf. Koehler, Z. A. ix. 1886. 



1 An invagination in the development of the ventral cord possibly takes place in some Chae- 

 topoda, and it is difficult to assign any other origin to the canal which traverses the cord in the 

 Gephyrea chaetifera. It is doubtful whether such an invagination per se can be held to have a 

 phylogenetic significance. The point can only be determined by future investigation. 



