310 



ENTEROPNEUSTA FROM THE SOUTH PACIFIC, 



It is perhaps not out of place to enquire whether there is any parallel instance of a 

 minute, toothless, buccal orifice facing upwards. One of the most remarkable Teleostean 

 fishes I have ever seen, namely, Amphisile strigata Guenther', has the habit which I 

 observed for the first time near Dawson Straits in the D'Entrecasteaux Group (British 

 New Guinea), of swimming in an upright position in the water by means of its pectoral 

 fins. The caudal and pelvic fins are vestigial. The entire ventral surface from tip to 

 tail is as sharp as a knife-edge. The animal is pointed at both ends, about six inches 

 long, one inch maximum height and J-inch maximum thickness along the back. It cuts 

 through the water with its razor-edge at a great rate, and the mouth is an extraordinarily 

 minute terminal toothless orifice pointing upwards in consequence of the erect swimming 

 attitude. 



III. Regional Pores and Nephric Tubules. 



Bateson was the first to compare the proboscis pore of Balanoglossus with the orifice 

 of the praeoral pit of the larva of Amphioxus, basing the comparison upon Hatschek's 

 account of the origin of the praeoral pit from the left division of the head-cavity. In 

 view of the uniquely amphioxine nature of the origin of such a structure as the praeoral 

 pit, combining the properties of gland and sense-organ, from a coelomic pouch ; also in 

 view of recent attempts to discredit Hatschek's discovery, a few general aspects of the 

 question may be brought into view. 



In the first place it is quite certain that one's morphological sense of coelomic 

 propriety would never have been offended if the left head-cavity had acquired a com- 

 munication with the exterior by means of a minute pore (which might perhaps have 

 been difficult to find in section) instead of by a generous embouchure. 



In the second place it is well to remember what seems to be usually forgotten, 

 namely, that Hatschek's discovery was the result of unbiassed observation and no 

 theoretical consequences were made to hang upon it until Bateson made the comparison 

 referred to above. 



Lastly Hatschek's account of the origin of the praeoral pit, which was based upon 

 observations upon the living embryos, has recently been confirmed in section by 

 MacBride-. 



It is much easier to unravel the anterior trematic complex of the Ascidian larva 

 than that of Amphioxus. In the larva of Amphioxus we have mouth, praeoral pit', 

 neuropore, and Kdllikers olfactory pit which arises as an epidermal depression over the 

 neuropore. The olfactory pit is the disturbing element. The most obvious conclusion is 

 that it is comparable with Spengel's anterior Epidermistasche in the Enteropneusta, but 

 I do not think this is quite the right conclusion. Neither do I think that the com- 

 parison of the proboscis-pore with the orifice of the praeoral pit is as simple a matter 



1 Kindly identitied for me by Mr G. A. Boulenger, F.R.S. 



E. W. MacBride, "The early development of Amphioxus," Q. J. M. S., Vol. xl., 1898, p. 589. 

 ^ The praeoral pit itself undergoes a certain amount of differentiation, but this does not directly concern 

 us now. 



