Papers from the Marine Biological Laboratory at Tortugas. 207 



membranes and he failed to observe the very evident centrosomal crescent 

 at one end of the spermatozoon. 



The adult apyrene spermatozoon of Stromhus is composed of a central 

 spindle-shaped body, which is long and narrow and slightly flattened dorso- 

 ventrally, on the sides of which are attached two broad undulating mem- 

 branes (fig. 6). At the anterior end of the cell-body there is a crescent- 

 shaped plate of centrosomal origin ; starting from the horns of this crescent 

 the undulating membranes round out quickly to their maximum width, 

 while posteriorly they gradually become narrower and finally end in a 

 short, sharply pointed tail-piece. In the membranes, here and there, can 

 be seen indications of the fibers of which it is composed, but both these and 

 the centrosomal plate are brought out more distinctly in fixed and stained 

 specimens. 



The interior of the cell is filled with a number of large secreted polygonal 

 bodies composed of an albuminous substance or substances, possibly of a 

 deutoplasmic nature like the yolk granules in the nurse-cells in the testis of 

 Littorina (Reinke '12). When treated with iodine these bodies fail to give 

 the reaction for starch or glycogen. When a mass of apyrene spermatozoa 

 are separated from the eupyrene and are subjected to the xanthoproteic 

 test, there is a very strong and clear reaction indicating the presence of 

 albumen. In sections stained with iron haematoxylin the secreted bodies 

 show the characteristic " Spiegelfarbung " of yolk granules. These bodies 

 are more or less regular in shape and position but they decrease in size toward 

 either end of the cell. In the living spermatozoon, at its posterior end, 

 there can be seen a small aggregation of mitochondria. No traces of nuclear 

 material can be found except in fixed specimens; here they appear as occa- 

 sional darkly staining granules of degenerating chromatin lying between the 

 albuminous bodies. 



The orientation of the apyrene spermatozoon has been established upon 

 morphological grounds. In Paludina, that end of the oligopyrene sper- 

 matozoon which contains the remains of the nucleus, i. e., the head, has 

 been designated as anterior and this, too, is the end toward which the axial 

 fibers have grown. As there is no nuclear head in the apyrene spermatozoon 

 of Stromhus, the direction of growth of the axial fibers must determine the 

 poles of the cell. The blunt, rounded end is the one toward which the 

 fibers have grown and is therefore anterior, while the narrow pointed one is 

 posterior. In movement it is the morphologically posterior end of the 

 spermatozoon which is usually directed forward, although occasionally the 

 reverse is seen to occur. 



The movement of the spermatozoon is caused by contraction waves 

 which pass alternately down the two membranes. At first these contraction 

 waves are long and slow, propelling the spermatozoon with an even, steady 

 motion. They usually pass down the membranes in a postero-anterior 

 direction, but occasionally a reversal takes place; it is then that the sper- 

 matozoon is seen to move with its anterior end directed forward. The 



