236 Papers from the Marine Biological Laboratory at Tortugas. 



posterior portions of the cell have been completely filled with them and all 

 of the chromatic vesicles have disappeared. 



11. In the meantime, the bundle of axial fibers continue to grow until 

 the cell has been elongated in an anterior direction, along its chief axis, by 

 about one-third its original diameter. Afterwards, the continued growth of 

 the axial fibers is not accompanied by a fully compensating increase in the 

 length of the cell ; the changes which ensue are all the direct result of this fact. 



12. A longitudinal split occurs in the bundle of axial fibers, dividing it 

 into two equal halves, each of which moves in an opposite direction towards 

 the surface of the cell. In doing so they rupture the ring of dense cytoplasm 

 which lie around the base of the bundle. This substance gradually disap- 

 pears, but the mitochondria associated with it persist in the adult apyrene 

 spermatozoon. 



13. Having reached the surface of the cell, the secondary bundles of 

 axial fibers now come to extend laterally beyond it. The further growth 

 of the fibers causes a number of folds to occur throughout the length of the 

 bundles. Finally a general elongation and constriction of the cell occur, 

 with the result that the body of the spermatosome acquires the spindle-like 

 shape of that of the adult apyrene spermatosome and the secondary bundles 

 on both sides of it become straighter and more flattened, forming the 

 undulating membranes. 



14. In the writer's opinion the apyrene spermatozoa of Stromhus sub- 

 serve their purpose after copulation has taken place and their function is 

 connected with the katabolic changes which they undergo. Their behavior 

 may be explained on the grounds of the following three suggested possi- 

 bilities: {a) They may serve as nurse-cells to the eupyrene spermatozoa 

 after copulation and before the latter reach the seminal receptacle; {h) they 

 may, by the liberation of some substance, stimulate the eupyrene sperma- 

 tozoa or the eggs or both during fertilization; or, by the liberation of some 

 substance to which the eupyrene spermatozoa are negatively chemotactic, 

 they may act as an aid in the final disposition of the latter. 



15. The conditions met with in the uterus and seminal receptacle of the 

 female after copulation has taken place and before oviposition has com- 

 menced show that the apyrene spermatozoa do not participate as such in 

 the fertilization of the egg. 



BIBLIOGRAPHY. 



AUERBACH, L. 



1896. Untersuchungen ijber die Spermatogenese von Paludina vivipara. Jenaische 

 Zeitsch. f. Naturw., Bd. xxx, N. F. xxiii. 

 Brock. 



1887. Ueber die doppelten Spermatozoen einiger exotischer Prosobranchier. Zool. 

 Jahrb., Bd. n. 

 V. Brunn, M. 



1884a. Untersuchungen iiber die doppelte form der Samenkorper von Paludina vivipara. 



Arch. f. mikr. Anat., Bd. xxni. 

 1884&. Weitere Funde von zweierlei Samenkorper in demselben Tier. Zool. Anz., Bd. vii. 



