152 



BIOL OGICA L L ECTURES. 



not such as to cause the extensive retro^n-essive development 

 which they are supposed to have undergone and which it is 

 assumed has affected nearly all of the organs of the body. 



It seems to have become a settled belief among the large 

 majority of zoologists of both morphological and systematic 

 proclivities that the number of gills found among vertebrates 

 never rises above eight pairs in existing forms. The few who 

 have recognized the true state of the case have had little to do 

 with the education of the younger men, and so the error has 

 continued to be taught. Lankester ^ wrote in 1 890 — regarding 

 the gills of vertebrates, "The pharyngeal slits follow closely 

 upon the mouth, and in existing Craniata never number more 

 than eight pairs." Wiedersheim ^ gives seven pairs of gills as 

 the largest number occurring among craniate vertebrates, while 

 Claus, Huxley, Jackson-Rolleston, Hertwig and others give the 

 number varying from 5 to 8, but never greater than 8. They 

 evidently confine themselves to Miiller's statement concerning 

 the number of gills {^-J) in Myxinoids and to the known facts 

 concerning Petromyzoa (7) and the Notidanidae {6-7). In 

 1854 Charles Girard described a fish from the coast of Chili 

 which he called Bdellostoma polytrema, and which lie found to 

 have 14 pairs of gills. In 1873 Putnam found that the 

 Bdellostomas of the Hassler expedition, collected off the coast 

 of Chili, had 10 pairs of gills. Later on Lockington (1878) 

 described a similar fish from San Francisco which had 1 1 pairs 

 of gills. These are the only original observations, wdth which I 

 am acquainted, which give the number of Myxinoid gills greater 

 than the accepted numbers (6-7). Yet these facts have been 

 many times confirmed by such men as Gunther, 1873, Gill. 

 1880, and Jordan and Gilbert, 1882, who gave the number of 

 gills of the Pacific Bdellostomid as 1 1-14. Notwithstanding all 

 these published accounts, morphologists have completely over- 

 looked these facts, and while speculating on the ancestral 

 number of gills of vertebrates, have depended for the most pari 

 upon the embryological stages of Elasmobranch and Teleost 

 fishes. 



1 I-incy. Brit. Article on vertebrates. 

 * Grundriss d. vergl. Anat. Jena, 1S93. 



