xvi CYCLOSTOMATA 423 



in the mud of the sea-bottom at depths ranging to nearly 350 

 fathoms. They are able to swim very rapidly in an undulatory 

 eel-like fashion. M. glutinosa may grow to a length of nearly 

 two feet. The Hag has been described as a protandrous herma- 

 phrodite, that is, it is first a male and then a female, the gonad 

 of the young first producing spermatozoa, and at a later period 

 becoming an ovary arid giving rise to eggs. Tbis view has 

 hitherto met with general acceptance, but it has recently been 

 urged with some force that the presence of the two kinds of sex- 

 cells in a young animal is no proof of functional hermaphroditism, 

 since it is not uncommon " to find immature eggs in the testis 

 of many Vertebrates (Teleosts, Petromyzon, Amphibia), where the 

 assumption of hermaphroditism, to say nothing of its protandric 

 form, is entirely unwarranted." 1 Myxine produces eggs similar 

 to those of Bdellostoma. Nothing is known of its breeding 

 habits, or of its embryology. 



Fam. 2. Bdellostomatidae. Gill-sacs 6-14 pairs, all with 

 separate external orifices. Bdellostoma (Fig. 92, B) is found on 

 the Pacific sea-board of both North and South America, at the 

 Cape of Good Hope, and on the coasts of New Zealand. The 

 numerical variation of the gill-sacs in different species, and in 

 different individuals of the same species, and even on opposite 

 sides of the same individual, is very remarkable. Out of 354 

 examples of the Californian species (B. stouti) examined by 

 Dr. Ayres, 2 101 had 11 gill-sacs on each side; 26 had 11 on 

 one side and 12 on the other; 208 had 12 on each side; 

 11 had 12 on one side and 13 on the other; and 8 had 

 13 on each side. Occasional specimens may have 14 gill-sacs 

 on each side. The variations are apparently quite independent 

 of size, age, or sex ; and when the gill-sacs are asymmetrically 

 developed, the additional sac may be either on the right side or 

 on the left. In the Chilian species there are 10 gill-sacs on each 

 side, but in the species from the Cape of Good Hope the number 

 is reduced to 6 or V. Bdellostoma closely resembles Myxine in its 

 habits and mode of feeding. The Californian species attaches 

 itself to the gills or to the isthmus of large Fishes, and then 

 rapidly bores its way into the body, devouring the viscera and 

 muscles but leaving the skin intact. It usually attacks large 



1 Bashford Dean, Kupffer's "Festschrift," Jena, 1899, p. 227 et seq. 

 2 Journ. Morph. xvii. 1898, p. 213. 



