Oogenesis and Fertilization of Grantia cornjjressa, 281 



described by Jorgensen and Dendy were mitochondria. In my 

 previous work on the oogenesis of Grantia I found what I con- 

 sidered to be true yolk, and confirmed tlie previous descriptions by 

 Jorgensen and Dendy of the presence of the " chromidia." I have 

 pointed out that these bodies should not be called " chromidia," for 

 they are not related to true chromatin. I still have doubts as to 

 whether the yolk granules, the " chromidia," and the Golgi bodies 

 are the only formed structures to be found in the sponge egg ; and 

 had it been possible I should have ) iked to have made many further 

 trials with modified mitochondrial methods to try to detect a finer 

 granulation which might be something apart from Jorgensen's 

 " chromidia," which at present I believe to be the mitochondria. 

 The only points which make me doubt an interpretation of these 

 ^' chromidia " as mitochondria are : — 



(a) Nucleolar " chromidia " (so-called) and true mitochondria 



both exist in Saccocirrus. 



(b) The fixing reactions of the sponge " chromidia " are not 



exactly similar to those of most metazoon mitochondria. 



Of course, neither of these points may signify, but I have tliought 

 it necessary to bring them forward. It should be remarked that 

 the archiannelid oogenesis is probably unique in the animal 

 kingdom, and the " chromidia " of the sponge in later stages of 

 oogenesis approximate closely to the fixing reactions of the mito- 

 chondria of other animals. 



Addendum I. 



Dr. Bidder, of Cambridge, showed me recently a preparation of 

 Sycon to illustrate what he calls " dolly " cells. One slide impressed 

 me very much because it showed two large cells partly protruding 

 from a " cloaca," and to each of these cells was attached a much 

 smaller cell the expected size of, flagellate, and closely resembling 

 a sponge spermatid. I consider that these cells found by Dr. Bidder 

 might be changing spermatozoa which have become attached to 

 the large cells, though it would not be possible to give an opinion 

 of value until one had personally studied the material. 



Addendum II. 



A few months ago Mr. Julian Huxley showed me some of his 

 slides illustrating his work on sponges (6). As is well known 

 H. V. Wilson found that sponges could be strained through fine 

 gauze so as to separate their individual elements, and many of the 

 latter could come together again and regenerate to form a new 

 sponge (8). Mr. Huxley repeated Wilson's work, and among the 

 new sponges or regenerates procured by this method he found 



