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. JZ 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 and giving rise to eggs. This 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.”* Myaine 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,? 101 had 11 gill-saes 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 7. Bdellostoma closely resembles Myatne 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 seg. 
2 Journ. Morph. xvii. 1898, p. 218. 
