ABDOMINAL PORES. 267 



the persistence of the abdominal pores is difficult to account for ; 

 they must have undergone a change of function. It is as difficult 

 to say what this function is as to explain the fact that they have 

 disappeared in the Amphibia, which are certainly a very ancient 

 group, while they are again met with amongst Reptiles. 



In Protopterus the abdominal pores open in front of, and in 

 Ceratodus behind the cloaca. In Ceratodus their arrangement is 

 similar to that seen in Elasmobranchs, and they are always paired : 

 in Protopterus, on the contrary, they undergo numerous individual 

 variations ; as a rule only one is developed, and this lies on the 

 same side as the vent sometimes to the right, sometimes to the 

 left of the middle line, and opens either within or without the 

 sphincter of the cloaca. If both pores are present, they always 

 open within the cloaca, on its dorsal wall, behind the aperture of 

 the rectum. 



Gegenbaur considers that the abdominal pores are not homolo- 

 gous throughout the series of the Vertebrata, and that they must 

 be considered in relation with other structures more particularly 

 the generative organs. Rathke and Huxley have pointed out 

 that in the series of the Salmonidas a gradual disappearance of 

 the oviducts is observable, their function being undertaken by 

 abdominal pores. This would seem to indicate that the abdominal 

 pores present in female SalmonidaB are not homologous with those 

 of other Fishes (e.g. Cyclostomi, Elasmobranchii, Dipnoi). 



BIBLIOGRAPHY. 



AEBY, CH. Der Bronchialbaum der Saugethiere und des Menschen, Leipzig, 1880. 

 AYEES, H. Untersuchungen iiber die Pori abdominales. Morphol. Jahrb. Bd. IX. 



1884. 

 BRIDGE, T. W. Pori Abdominales of Vertebrata. Journ. of Anat. and Physiol. 



Vol. XIV. 

 FISCHER, J. G. Anatom. Abhandlungen iiber die Perennibranchiaten und Derotremen. 



Hamburg, 1864. 

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(Contains also a copious bibliography of the larynx in general.) 

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 HUXLEY, T. H. On the Respiratory Organs of Apteryx. Proc. Zool. Soc. 1882. On 



the Oviducts of Osmerus, with remarks on the relations of the Teleostean to the 



Ganoid Fishes. Ibid. 1883. 

 KOLLIKER, A. Zur Kenntniss des Baues der Lungen des Menschen. Verhandl. der 



med. Gesellsch. z. Wurzbu,rg. N. F. Bd. XVI. (Compare also the text-books of 



Anatomy of Quain, Aeby, Henle, Krause, &c.) 

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d. Wiss. zu Berlin, 1846, 1848. Eng. trans. (Bell), Oxford, 1878. 

 PARKER, T. J. On some Embryos of Callorhynchus antarcticus. New Zealand 



Journ. of Science, 1883, and Nature, Vol. XXIX. p. 46. 

 KATHKE, H. Zur Anatomie der Fische. Arch. f. Anat. und Physiol. 1838. 

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(This includes an account of the anatomy and physiology of the air-bladder.) 

 STRASSER, H. Die Luftsdcke der Vogcl. Morphol. Jahrb. Bd. III. 1877. 

 "WlEDERSHEiM, R. Das Respirations -sy 'stem der Chamceleoniden. Berichte der 



Naturforsch. Gescllachaft zu Freiburg i/B. Bd. I. Heft III. 1886. 



