UROGENITAL SYSTEM OF MYXINOIDS 119 



bendings or convolutions were present in the ducts of any of the 

 specimens. The later ad bending at the inter septal Unes is some- 

 what less than in Bdellostoma, which may be due to the fact 

 that the somites are larger in Myxine. In the adult Bdellostoma 

 the somites are approximately 5 mm. wide, while in Myxine 

 they are about 6.5 mm. 



The histology of the ducts of Myxine is practically the same 

 as those of Bdellostoma. The long columnar cells are arranged 

 in longitudinal ridges. In the youngest specimen studied 

 (Myxine no. 18) the ridges are not formed in the same manner 

 as in Bdellostoma. The basal membrane of the epithelium does 

 not bend inward, toward the lumen of the duct, at the base of 

 the ridges, hence no concavities are formed under the latter. 

 Also, the nuclei of the epithelial cells remain at the same level 

 around the entire circumference of the duct and turn inward 

 only very sHghtly at the base of the ridges. The ridges are 

 formed solely by the elongation of the epithelial cells. The 

 longest cells are approximately 0.0675 by 0.0081 mm. The 

 majority of the nuclei are round, although many are short 

 ovals. There are approximately fifteen ridges in each duct in 

 the mid-region of the body. 



In all the adult Myxines the ridges in the ducts are more 

 numerous, shorter and narrower than in BdeUostoma. Their 

 shape is shghtly different from those of the latter animal, and 

 much more uniform. They are usually narrower in the middle 

 than at the ends, and never have a wide, flat surface such as 

 are frequent in Bdellostoma. In one specimen, which has eggs 

 12 mm. long, the duct is 0.39 by 1.2675 mm., and has 54 ridges, 

 each approximately 0.039 by 0.117 mm. The duct of another 

 animal measures, at one place in the mid-region selected at ran- 

 dom, 0.2925 by 0.975 mm., and has 53 ridges, each approxi- 

 mately 0.029 by 0.105 mm. The ridges present a finger-like 

 appearance, as shown in figure 63. 



The epithehal ridges in the ducts of adult animals do not 

 have concavities beneath them, but the nuclei at the base of the 

 ridges are arranged in a small heap (fig. 63) . 



