EARLY DEVELOPMENT OF GEANTIA COMPRBSSA. 263 



now well known, some workers claim that the middle-piece of the animal 

 sperm breaks up during fertilization, and growing in the egg-cytoplasm 

 takes part in the phenomenon of amphimixis. 



En passant, I examined the various statements with regard to the origin 

 of the germ-cells in sponges. Dendy (2), in his late paper, supports 

 Haeckel's view that the germ-cells are formed from metamorphosed collar- 

 cells, a view which is strenuously opposed by the Neo-Weismannians. As 

 the work progressed, I found that two well-known spougologists, Jorgensen 

 and Grorich, had made an extraordinary misinterpretation of the early stages 

 in fertilization. This paper gives the first account of the peculiar fertiliza- 

 tion of the sponge and of the spermatogenesis of a marine sponge. 



3. Previous Work. 



There is no previous work on Grantia (Si/con) executed by any observer 

 acquainted with modern interpretation as to the bodies in the cell. There 

 are, however, several papers by earlier authors which are important ; I refer 

 to those of Grorich (6), Jorgensen (8a), Maas (10), and Dendy (2). Jan 

 Hirschler (8) has examined the collar-cells of Spongilla, while various other 

 authors have written papers on the development and larva;. The papers of 

 Gbrich and Jorgensen are reviewed by Dendy (2), and will only be mentioned 

 in the text when necessary. 



Maas (10) in Si/candra raphanus describes the maturation and fertilization. 

 The sperm penetrates the egg before the formation of the second polar body. 

 With regard to the entiy of the sperm, he says : " Der Spermukern zeigt 

 sich beim Eintritt bestehend aus einer einzigen dichten Chromatin masse von 

 Bohnenform und einem dahinter liegenden stark lichtbrechenden Korper, 

 beides umgeben von Zone verdichteten Plasmas mit sehr intensiver radiarer 

 Strahlung." The "stark lichtbrechenden Korper" is the " Chromidium " 

 of Jorgensen. The two pronuclei come to lie in the central region of the 

 ovum, chromosomes appear in each, and the first segmentation-spindle is 

 formed. Jan Hirschler (8) describes briefly the Grolgi body in the flagellated 

 cells of Spongilla. It lies beneath the collar, is spherical, and resembles that 

 of the central capsule (idiozome) in many metazoan germ-cells. This author 

 also notes small granules of mitochondrial nature. He describes no stages 

 in gametogenesis or development. Dendy (2), in a late paper, describes the 

 gametogenesis of Grantia compressa. He adopts Haeckel's (7) idea that 

 collar-cells can metamorphose into germ-cells. He describes oogenesis in 

 detail, deriving oogonia from collar-cells, " which accumulate reserve material, 

 enlarge, withdraw their collars and flagella, become amoeboid and wander 

 into the mesoglea, re-entering the chambers before dividing mitotically into 

 oogonia of the second generation/' Dendy finds " chromidisi "' in the oocyte 

 cytoplasm, which he thinks are formed by a " process of extensive chroniidium- 



20* 



