277 



IX. — Further Notes on the Oogenesis and Fertilization of 

 Grantia compressa* 



By J. Beonte Gatenby, B.A., B.Sc, D.Phil. (Oxon.), F.R.M.S., 

 Lecturer in Cytology and Senior Assistant in Zoology, 

 University College, London, and Senior Demy, Magdalen 

 College, Oxford. 



One Plate. 



Inteoductiox. 



So far as at present known the sponr^e is the only animal in which 

 the male element does not itself penetrate the egg directly, but 

 first enters another cell which is thereby induced to carry the 

 sperm to the expectant ripe oocyte. 



Precocious fertilization, such as occurs in Saccocirrus or Otome- 

 sostoma (->),t is a very peculiar process, but no carrier cell intervenes 

 between oogonium and spermatozoon, and so the process does not 

 introduce a third cell as in the sponge. 



In this paper I have described a stage hitherto missing from 

 my previous description {3), and I have taken the opportunity to 

 examine further the " chromidia " formation found by Jorgensen (7) 

 and Dendy {2). 



The First Stages of Fertilization in Grantia 



. compressa. 



In a previous paper I have described the peculiar fertilization 

 in a sponge, in which the spermatozoon enters a collar cell and is 

 thereby carried to the ripe oocyte. All the spermatozoa found in 

 collar cells were oval structures containing a bun-shaped reticu- 

 late nucleus and a similarly shaped mitochondrial middle-piece. 

 From some stages of spermatogenesis found by me in Grantia it 

 was known that the spermatozoon (spermatid) was provided with 

 a flagellum. It was concluded that the ovoid spermatozoa found 

 in the collar cells were somewhat changed in shape, a result due 

 to their presence in another cell, and that very probably the 



* The materials used in this research were purchased by a Government Grant 

 of the Royal Society. 



t The italic figures within brackets refer to the Bibliography at the end of 

 the paper. 



