26o FIELD. [Vol. XL 



3. The number of spermatozoa formed from a spermatogone 

 is four, by means of two mitotic divisions. 



4. Each mitotic division from the spermatogone to the 

 spermatid is a "reducing division," i.e., the number of chromo- 

 somes is reduced one-half by each division. 



5. The number of chromosomes in the spermatozoon is 

 nine. This number is characteristic for the Echinoderm 

 phylum. 



6. The nucleus of the spermatid contains chromosomes and 

 caryolymph. When this nucleus becomes the nucleus of the 

 mature spermatozoon chromosomes and caryolymph are not 

 distinguishable. They have either mingled to form a homo- 

 geneous mass, or else the caryolymph has been extruded. 

 The smaller size of the nucleus of the spermatozoon points to 

 the latter alternative. 



7. When the nucleus of the spermatozoon in the fertilization 

 process has passed the outer denser cytoplasmic portion of the 

 ovum it increases in size ; caryolymph and chromosomes appear 

 again. Hence, one would infer that the male pronucleus de- 

 rived its caryolymph from the cytoplasm of the ovum. 



8. The small refringent body seen by various investigators 

 at the apex of the head of the spermatozoon is shown to be 

 the centrosome. It is derived directly from the centrosome of 

 the previous generations of cells. It is extranuclear in posi- 

 tion in the spermatid and spermatozoon ; possibly intranuclear 

 in the spermatogone and spermatocyte. 



9. The sperm-centrosome, with its definite spherical outline, 

 consists of two sorts of substances, a denser central portion 

 surrounded by a clearer homogeneous mass. I have never 

 succeeded in finding the ^gg centrosome. 



10. The sperm-centrosome is very small in Crinoidea and 

 Echinoidea ; much larger in Holothurioidea, Ophiuroidea, and 

 Asteroidea. Since throughout it has the same optical appear- 

 ance and shows the same micro-chemical reactions as the 

 mitosome (Nebenkern ; Mittelstiick ; middle piece), and also 

 from a comparison with the conditions found elsewhere, particu- 

 larly in the Pulmonates (where in the spermatid the centrosome 

 is contained within the mitosome, but in the mature spermato- 



