18S8.] MORPHOLOGY OF SUPERNUMERARY PHALANGES. 495 



EXPLANATION OF PLATE XXIII. 



Fig. 1. Longitudinal section through the generative segments of an immature 

 esamjile of Clitellio arenarius. cp, spermatheca ; ;", testis ; ./', funnel 

 of vas deferens; v.d, \as deferens ; o, ovary; at, atrium ; ov, funnel 

 of oviduct. 



2. Longitudinal section through the oviducal funnel of a mature Cli- 



tellio arenarius. od, oviducal funnel, above is the body-wall ; the 

 epiderm in this (the clitellar) region consists of tall cells closely 

 packed with granules. 



3. Portion of a seminal sac of the same species, v, wall of the vescicle ; 



bl, blood-vessel ; s, developing spermatozoa. 



4. An egg-sac of the same worm, containing a single ovum ; hi, blood- 



vessel in wall of sac ; the smaller black dots are nuclei of the con- 

 nective or muscular tissue which forms the wall of the sac ; the 

 ovum is mature and full of yolk-spherules. 



5. Transverse section through vas deferens of Clitellio arenarius ; this 



figure is drawn to the same scale as the following, with wliich it 

 may be compared. 



6. Transverse and longitudinal sections through vas deferens of Hemi- 



tuhifex benedii. Drawn to the same scale as fig. 5. 



7. Heviitubifex benedii, section to illustrate structure of atrium, &c. 



at, atrium ; v.d, vas deferens dilated above, near to its junction with 

 atrium ; pr, prostate. 



8. Section through penis and penis-sheath of Hcmitubifex benedii. 



p, penis with chitinous covering. 



9. Section through penis and penis-sheath of the same species at a point 



further removed from the external orifice ; the penis (p) is seen to 

 be independent of the penis-sheath, which lies to the left-hand side. 



3. Observations upon the Morphology and Genesis of 

 Supernumerary Phalanges^ with especial reference to 

 those of the Amphibia. By G. B. Howes, F.Z.S., 

 F.L.S., Assist. Prof, of Zoology, Normal School of 

 Science and R. School of Mines, S. Kensington, and 

 A. M. Davies, Assoc. N.S.S. 



[Keceived December 4, 1888.] 

 (Plates XXIV. & XXV.) 



CONTENTS. 



I. Intuoductoey, p. 495. 

 II. General and Anatomical, p. 496. 



III. Histological and Developmental, p. 499. 



IV. Individual and Classificatoey, p. 501. 



A. Phaneroglossa. 



B. Aglossa. 



C. Urodela. 



V. General Consideeations, p. 506. 

 VI. Conclusions, p. 509. 

 VII. List of Memoirs and Papers referred to, p. 510. 

 VIII. Explanation of the Plates, p. 511. 



I. INTRODUCTORY. 



There appeared in the second part of this volume a short paper 

 (2) by Boulenger, in which the author verified and extended an earlier 



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