306 NATHAN FASTEN. 



EXPLANATION OF PLATE 4. 



FIGS. 48 to 53. Successive stages in the transformation of the spermatid, 

 resulting in the primary vacuole (z>) being formed at one pole, while the nucleus 

 (K) occupies the opposite pole, and in between them the mitochrondria-like mass 

 (m) and the centrosome (c) take their position. 



FIG. 54. The secondary vacuole (z/) makes its appearance at the distal end of 

 the first vacuole (z/). 



FIGS. 55 to 58. Stages in the transformation of the spermatid in which the 

 primary and secondary vacuoles transform into distinct vesicles, and the central 

 body (b) assumes a dumb-bell appearance. 



FIGS. 59 to 62. Spermatid transformations showing the hollowing out of the 

 distal end of the central body; the formation of the chromatin-ring (d), and the 

 fusion of nucleus and mitochondria-like mass into a nuclear-mitochondrial cup (h). 



FIGS. 63 and 64. Formation of the rays (r) of the spermatozoon. 



FIGS. 65 and 66. Side and bottom view of mature spermatozoa, showing details 

 of structure. 



FIG. 67. Spermatophore, filled with mature spermatozoa. 



FIGS. 68 and 69. Three- and four-rayed types of spermatozoa, as seen suspended 

 in the body fluid of Cancer magister. 



FIGS. 70 to 78. Successive stages in the explosion of the mature spermatozoon 

 when surrounded with salt solutions of lower osmotic density than sea water. 



FIG. 79. Spermatozoon which has exploded in distilled water. 



FIG. 80. Exploded spermatozoon in which the secondary vesicle has com- 

 pletely disintegrated. 



