214 PERCY SLADEN TEUST EXPEDITION, 



Asymmetron has not yet been found in the adult state anywhere in the Indian Ocean, 

 except in the Maldive Archipelago. Mr. Stanley Gardiner informs me that he made 

 special search for it, without success, in the Chagos and Seychelles Archipelagoes, and off 

 Mauritius and Madagascar, and that Mr. Fryer has failed to find it at Aldabra. Such 

 negative evidence need not, however, have great weight against the belief we have 

 expressed above. A. pelagicus must develop into an adult of some kind, and any other 

 Cephalochordate which can claim to be that adult is at present quite as unknown from 

 the region as Asymmetron itself. 



Goldschraidt's Amphioxides stermirus, with its great similarity to A. pelagims, is very 

 probably only a variety, and therefore need not detain us. 



The third species, A. valdivice, agrees approximately as regards its myotome formula 

 with Heteropleuron parvum, a genus founded by Parker (1904) on two specimens from 

 the Maldives. The somewhat blunt notochord and the m.anner in which the myotomes 

 end off posteriorly, are points of resemblance between the two. H. parvum, however, is 

 described as possessing ventral fin-ray spaces and fin-rays, and is also remarkable for its 

 small size (11'5-12'5 mm.). It would seem improbable therefore that its larva could 

 attain, a size of 10'6 mm. without showing traces either of gonads or of ventral fin-ray 

 spaces. It is perhaps rather more probable that A. valdioice belongs to H. agassizii, 

 which is distinguished from all other sjiecies of Heteropleuron by the absence of 

 ventral fin-ray spaces. Since only a single specimen of this has been described, the fact 

 that it possessed as many as 60 pre-anal myotomes need not exclude the possibility. 

 The extension of the dorsal fin-ray spaces as far as the anterior end of the nervous 

 system certainly allies A. valdivice to Heteropleuron rather than to Asymmetron : as 

 to its specific assignment we must for the present suspend judgment. 



Goldschmidt obtained both A. pelagicus and A. valdioice off the West Coast of Africa, 

 the Cephalochordate fauna of which is at present practically unknown. Probably, 

 therefore, the adults to which they belong will one day be found there, and we may look 

 to future collections from this region, from the West Indies (Bahamas), and from the 

 Indian Ocean (in particular the Maldives) for the final settlement of the nature of 

 " Amphioxides." We may further expect that new kinds of " Amphioxides" will be 

 discovered. Not improbably all the species of Heteropleuron and Asymmetron — possibly 

 some Branchiostoma as well— may have pelagic larvae of the same type. The name 

 itself nmst disappear as tbat of a genus, but may conveniently be retained as an 

 expression for the peculiar type of larval organisation brought into prominence by 

 Goldschmidt's monograph. 



TO WHAT EXTENT IS " AMPHIOXIDES" PRIMITIVE? 



By his researches on Amphioxides, the comparison of its structure with that of the 

 JBrancMostoma larva, and the consideration of the developmental history and so-called 

 " metamorphosis " of the latter, Goldschmidt was led to the remarkable conclusion that 

 Amphioxides — and the .Z?rrt«eA/oi/o/Hrt larva to a lesser extent — showed the primitive type 

 of organisation from which the advilt organisation of all other known Cephalochordates 



