BDELLOSTOMA DOMBEYI, LAC. 



145 



separated by a notch in the lower edge of the fold. The left 

 organ seems never to be developed in any of the Myxinoids. 

 In all cases, so far as my observation goes, each individual is 

 potentially bisexual, but Bdellostoma is not much like the 

 Myxine in changing its sex with increase of age ; certainly this 

 condition does not seem to be so clearly expressed in Bdellos- 

 toma as in Myxine. For whereas in Mixine only the young 

 animals seem to be males, in Bdellostoma large and presumably 

 old animals are found to be males as well as females, and both 



.t 



FIG. 10. A view 

 similar to that shown 

 in Fig. 9, but drawn 

 from a 7-7 gilled 

 Bdellostoma. Let- 

 tering the same. 



FIG. ii. The branchial 

 apparatus of Myxine, seen 

 from the ventral face, to 

 show what the changes are 

 which have made Myxine's 

 respiratory tract so differ- 

 ent from Bdellostoma's. It 

 is at once apparent that the 

 only structures in any way 

 changed are the external 

 branchial tubes, which, by 

 all uniting together, have 

 only to pierce the skin at 

 one place, a?., oesophagus, 

 1-6 and g. s., the branchial 

 sacks, br. /., the external 

 branchial tubes of the first 

 gill. Z>, the short duct 



formed by the union of all the gill tubes of 



one side. 



sexes are found among the smallest individuals taken. The 

 large anterior region of the peritoneal fold is always ovary, while 

 the much smaller posterior region of the fold is the testicular 

 region. The ovary is readily distinguished by the numerous 

 eggs in many stages of development, while the testicular part, 

 which is separated from the ovarian part by a notch or deep 

 scallop cut in the border of the fold, is to be distinguished by 

 its clear vesicles, grouped together like a bunch of grapes. 

 Of course a crucial test of the character of the small vesicles 

 is the presence of spermatozoa in the testicular part. Tested 

 in this way many individuals were found to be ripe, while 

 among the females very few were found to contain eggs in 



