56 BULLETIN OF THE 



diately invest the ovum. He does not expressly state this, but it seems 

 to me he leaves one to draw such an inference. He says that the 

 ovarian egg when 0.6 mm. in diameter is surrounded by a single layer 

 of very flat polygonal cells, outside of which is a thick layer of fibrous 

 connective tissue, and that when the eggs have attained a length of 

 18 mm. and a thickness of 6 mm. there are two connective-tissue 

 envelopes ; an outer thinner, a continuation of the mesovarium, and 

 an inner, which at the ends of the egg is thickened (0.4 mm.) and 

 vascular. At its inner surface the inner membrane is condensed into 

 a lustrous membrana propria 2 /x thick, and is firmly attached to the 

 underlying "Testa." In contact with the inner surface of this mem- 

 brana propria is a layer of cells. In the middle of the egg the cells are 

 cubical, but they become more and more cylindrical towards its poles, 

 where the layer becomes three or four cells deep. 



I believe there can be no question that this layer of cells inside the 

 membrana propria represents the granulosa ; but it seems as though 

 Muller must have overlooked the egg membrane, if one existed at that 

 stage, and must have taken the granulosa to be in some way the equiva- 

 lent of it. Perhaps, assuming that the granulosa cells secreted the 

 membrane, his idea was that the granulosa ought itself to be considered 

 as a part of the "Testa," for he afterwards (p. 126) mentioned, in the 

 case of Petromyzon Planeri, "a very thin folded egg membrane which 

 exhibited a polygonal pattern when seen from the surface." Moreover, 

 he says, with regard to two deposited eggs of Myxine which he examined, 

 that there was no trace of either inner or outer connective-tissue en- 

 velope, and from this fact concludes that they must have undergone 

 complete regressive metamorphosis, similar to that which the enamel 

 organ of the teeth suffers after the completion of the enamel. 



W. Muller is the only person who has seen anything of a micropylar 

 apparatus in the myxinoids. " Exactly in the middle of the white pole 

 of the egg, n he says (p. 115), "this cell layer [granulosa] exhibits a 

 conical infolding 0.1 mm. deep and 0.06 mm. broad, which contains a 

 funnel-shaped opening, the micropyle, which is directed straight toward 

 the underlying nucleus and the protoplasm surrounding it." This is 

 the whole of his description ; and from it I infer that he has seen that 

 portion of the granulosa which occupies the micropylar funnel, but that 

 the micropylar canal — which is a passage through a membrane, not an 

 involution of a cell layer — has not been seen by him. If the condition 

 in Myxine is at all comparable with that in Lepidosteus, it is certain 



