148 



BIOL OGICA L L E C TURES. 



one of the vertebrate type of organization, and the body ever 

 after remains in this inferior condition of structure, though it 

 produces germs which in their development attain the higher 

 level of vertebrate organization, only to sink back to the lower 

 level of Tunicate structure. 



Fig. 13. — A view of three ripe eggs of Bdellostoma dombeyi, showing their 

 natural size, the variations in shape, the manner in which they hold together by 

 means of their anchor hooks, and the position of the suture which allows of the 

 ready separation of the cap from the body of the egg membrane, a, an end view 

 of an egg cap. The anchor filaments have all been radially spread to show the 

 spiral arrangement of the filaments upon the cap surface, x, the anchor head. 

 /, the filament, b, a side view of another cap. st, the cap membrane. /', the 

 row of enlargements forming the bases of the filament.s, f. .r, the anchor heads. 

 The central dot in a shows the position of the micropylar funnel which leads into 

 the micropylar canal. The egg membrane is composed of a thin genuine vitelline 

 memljrane and a thick corneous follicular (granulosa) membrane, and the anchor 

 threads are hollow evaginations from the end parts of tlie latter. Natural size, 

 a and b 'X 2 diameters. • 



1 .\fter a study of the development and the adult condition of the egg mem- 

 branes in Bdellostoma dombeyi I am certain that Cunningham is in error in calling 

 the egg membrane of the Myxinoids a vitelline meml)rane. Tlie corneous part of 

 the egg .shell is cellular in nature and the cell remnants are to be seen in the ripe 

 egg .shell. The anchor hooks are formed by the evaginations of this granulosa 

 layer in late stages of egg life, due to the outgrowth of solid rods of the vitelline 

 membrane. These rods appear to be resorbed before the ripening of the egg and 

 thus the anchor filaments are left hollow. The My.xinoid egg is thus very much 

 like other fi.sh eggs as regards its envelopes. .\n illustrated account of these 

 facts, among others is ready for the press. 



