576 R. RAY LANKMSTER. 



not occur until after ancestral forms witli one, with two, and 

 with three prosthomeres had come into existence. On the 

 whole the facts seem to be against this supposition, though 

 we need not suppose that the gnathobase was very large or 

 the rami undeveloped in the buccal parapodia which were 

 destined to lose their mandibular features and pass in front 

 of the mouth. 



References. 



1. Bateson. — 'Materials for the Study of Variation' (Macmillan, 1894), 



p. 85. 



2. Lankester. — "Primitive Cell-layers of the Embryo," 'Annals and Mag. 



Nat. Hist.,' 1873, p. 336. 



3. KoRsciiELT and Heider. — ' Entwickelungsgescliichte ' (Jena, 1892), 



cap. XV, p. 389. 



4. ]*'oLSOM. — "Development of the Mouth Parts of Anurida," 'Bulletin Mus. 



Comp. Zool. Harvard College,' vol. xxxvi. No. 5, 1900, pp. 142—146. 



5. Lankester. — "Observations and Reflections on the Appendages and 



Nervous System of Apus cancriformis," 'Quart. Journ. Micr. Soc.,' 

 vol. xxi, 1881. 



6. lIoFER. — "Ein Krebs mit einer extremitat statt eines Stielauges," 'Yer- 



handl. d. Deutsclien Zool. Gesellsch.,' 1894. ..r^ 



7. Watase. — "On the Morphology of the Compound Eyes of Arthropods," 



'Studies from the Biol. Lab. of the Johns Hopkins University,' 

 vol. iv, pp. 287—534. 



8. Benham describes backward shifting of the oral aperture in certain Chseto- 



pods, 'Proc. Zoolog. Soc. London,' 1900, No. Ixiv, p. 976. 



N.B. — References to the early literature concerning the group Arthropoda 

 will be found in Carus, 'Geschichte der Zoologie.' The more important 

 literature up to 1892 is given in the admirable treatise on Embryology by 

 Professors Korschelt and Heider. 



