J USE M, 1895.] 



SCIENCE. 



('.47 



the most importaut data ivspecting the lan- 

 celets was urgent. Mr. "Willey's volume to 

 a very large extent administers to this 

 need. He lias judiciouslj' eomlnned the ob- 

 servations of himself and others and classi- 

 fied them under (I.) 'Anatomy ofAmphi- 

 oxus' and (II.) 'Development of Amphi- 

 oxus ; ' under the former caption, he has 

 data ' Historical,' on • Habits and Distri- 

 bution," 'External Form,' and 'Internal 

 Anatomj- ; ' under the latter he treats of the 

 ' Embryonic Development ' and ' Larval 

 Development,' enunciates certain ' General 

 Considerations,' and concludes with a com- 

 parison of 'Amphioxus and Ammoccetes.' 

 "We need only refer speciallj' to the section 

 on • The Excretory System' (pp. oo-~'y), 

 because it contains information on 'organs' 

 which wei'e long undiscovered, or at least 

 not appreciated. Mr. Willey is ' convinced 

 as to the essential identity of the excretory 

 tubules of Amphioxus with the pronephros 

 of the craniate vertebrates.' The informa- 

 tion respecting other structural features are 

 up to date and the inferences as to homolo- 

 gies and functions reasonable and jiulicious, 

 although there maj' be occasion sometimes 

 (but rarely) for dissent. But we could 

 have wished that the radical differences 

 between the lancelets and true fishes had 

 been emphasized by the use of terms indi- 

 cating that analogous parts were not homo- 

 logous. For instance, Mr. Willey correctly 

 states that there is a dorsal fin ' supported 

 by a series of gelatinous Jin-rays, each of 

 which lies in a chamber of its own,' and fur- 

 ther saj's that ' the ventral portion of the 

 tin in the region between atriopore and 

 anus is supported by a similar series of fin- 

 rays, but there are two of them placed side 

 b}- side in each compartment.' Such struc- 

 tures are verj- unlike the specialized rays of 

 teleostomous fishes, and to avoid the mis- 

 leading tendency of such terms it has been 

 recentlj' proposed to designate the so-called 

 ravs of the lancelets actinomimes and their 



inclosing chambers actlnotlomeit, while the 

 compound ventral fin has lieen designated 

 as the sifmpodium. Such terms will be use- 

 ful in systematic zoology as well as mor- 

 phology. 



The ground is now prepared for further 

 advance, and one of the first of the prob- 

 lems that need examination is the amount 

 of variability among the Branchiostomids. 

 The first preliminary is the dift'erentiation 

 of known variation into generic and specific 

 characters, instead of confounding all under 

 one generic name, as Mr. AVilley has done. 



Applying the mode of valuation current 

 for the higher groups, we have several 

 modifications of diflerent systems that are 

 available for genera. Such are the develop- 

 ment of the hinder end, the unilaterality 

 or bilaterality of the gonads or sexual organs, 

 the coordinate development of the meta- 

 pleural folds, the presence or absence of a 

 sympodium, and the development of the 

 dorsal fin, and especially the relative extent 

 of the actinomimes and actinodomes. Vari- 

 ations in these structures are expressible 

 under five generic terms already named, 

 Bra n chioitoma , Pa ra mph ioxtis, Epigon ich thys, 

 Asymmetron and Ainphioxida. Two of tiie 

 genera (Paramphio.rm and Epif/07iichthy$) 

 have recentlj' been combined in one to 

 which the new name Heteropleuroii has been 

 given, but even if such a union is favored, 

 Epigonichthys should be used as the first dis- 

 tinctive name given to a member of the 

 group; the two, however, appear to be suffi- 

 ciently distinguished by the fins. Epigo- 

 nichthys has an unusually high dorsal mem- 

 l.rane and contracted actinomimes. 



Eight species of lancelets are recognized 

 by Willey, as had been previously by Dr. E. 

 A. Andrews; one described in 1N89 (' J5. 

 pelagicum ' ) was overlooked and another 

 (Paramphioxm Singaleiim or Heteropleuroii 

 Hingaleme) has been described since.* 



*0n the species of Amphioxus. By J. W. Kirkaldy. 

 Rep. Brit. A.SS. AJv. So., 1894, pp. 685-686. 



