366 ON THE POISON-ORGANS OF TRACHiNUS. [June 19, 



11. GtJNTHER, A. The Study of Fishes. Edinburgh, 1880, 



p. 464. 



12. GiJNTHER, A. Article " Ichthyology " in Encycl. Brit. vol. xii. 



1881, p. 666. 



13. GuNTHER, A. On a Poison-organ in a Genus of Batrachoid 



Fishes. Proc. Zool. See. 1864, p. 155. 



14. Gressin, Leon. Contributions a I'etude de I'appareil a 



venin chez les poissons du genre " Vive " (Trachinus). These 

 de Paris, 4to. 1884. 



15. Kent, W. Saville. British Marine and Freshwater Fishes. 



Fisheries Exhibition Handbook, London, 1883, p. 29. 



16. Macalister, a. An Introduction to the Systematic Zoology 



and Morphology of Vertebrate Animals. Dubhn and London, 

 1878. 



17. Schmidt. Nord. Med. Arch. vi. no. ii. 1875. 



18. Seeley, H. G. Cassell's Natural History. Vol. v. London, 



1884, p. 92. 



19. Tybring, Oscar. Poisonous Fish (translated from the 



Danish by Hermann Jacobson). Bulletin of the United States 

 Fish Commission, vol. vi. 1886, p. 148. 



20. WiEDERSHEiM, R. Lehrbuch d. vergl. Anat. Jena, 1886, 



p. 20. 



21. WiEDERSHEiM, R. Comp. Anat. of Vertebrates (translated 



by W. N. Parker). London, 1886, p. 18. 



22. Yarrell. British Fishes. Vol. ii. pp. 3, 8. 



EXPLANAT[ON OF PLATE XVII. 



All the figures refer to Trachinus vipera. 



Fig. 1. The whole of the opercular apparatus, drawn from a transparent prepa- 

 ration mounted entire in Canada balsam. 



Fig. 2. The apex of the opercular spine, showing the manner in which it pro- 

 jects beyond its sheath. 



Fig. 3. A slightly oblique longitudinal section, taken about through the line 

 c-d in fig. 2. The epidermis has broken away, but the point at which 

 the cells of the gland were continuous with it is shown at x. 



Fig. 4. Transverse section through the opercular apparatus taken through the 

 line a-b in fig. 1. 



Fig. 5. Transverse section through the narrower part of the apparatus, near the 

 apex of the spine. 



Fig. 6. The 20th section posterior to (that is, nearer the apex of the spine than) 

 the last, passing through the region at which the involution of 

 the epidermis occurs (a-) ; the section is slightly obHque, and thus passes 

 through the involution at different levels on either side. 



Fig. 7. The 6th section posterior to the last, also passing through the epidermic 

 involution. 



Fig. 8. Transverse section through the first and second dorsal spines and 

 glands. The first spine being shorter than the second, the section 

 cuts it nearer the apex, through its narrower portion. 

 The sections were all drawn with the camera lucida to the same scale. 



LIST OF ABBEEVIATIONS. 

 ar. Articulation of opercular bone with hyomandibular. b.v. Blood-vessel. 



