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found a very general similarity, though in minor details there is 
considerable variation. The present preliminary account deals mainly 
with those general facts, which we have reason to believe obtain 
throughout the entire class, in those species which have retained 
the general and typical ontogeny. The spermatozoa in certain forms, 
particularly the Holothurids (e.g. Stichopus regalis; Cucumaria 
Planci) and Ophiurids (e. g, Ophioglypha lacetosa) are com- 
paratively large, and consequently much better adapted for study 
Taking advantage of this fact, and by the use of new apochromatic 
homogeneous immersion objectives I have been able to overcome many 
of the obstacles which have hitherto prevented an exclusive study of 
the spermatogenesis of the Echinoderms as a group. 
The account can perhaps be best arranged under three heads: 
(1) General Origin of the Spermatozoa. (2) Constituent Parts of the 
Spermatozoon. (3) The Origin of each Part. 
(1) General Origin of the Spermatozoa. 
We find that the largest cells, the spermatogenes (using the 
nomenclature proposed by LA VALETTE ST. GEORGE, and now very 
generally adopted) divide by mitosis, and form two spermatocytes. 
Next each spermatocyte divides, also by mitosis, forming two 
spermatids. Each spermatid then changes directly into the spermato- 
zoon, without further division. Thus each spermatogone gives rise 
to four spermatozoa. A favorable section of an alveolus of the 
testis shows distinct zones characterized by definite stages: e. g. near 
the periphery nearly all of the spermatogones have resting nuclei: 
next internally is a zone with the nuclei in active mitosis: next to 
these the spermatocytes; then the spermatids, and immature spermato- 
zoa, and finally in the center the mature spermatozoa. These zones 
are emphasized by those methods of technique which differentiate the 
actively dividing nuclei. 
My attempts to count the exact number of the chromosomes have 
thus far resulted unsatisfactorily owing to the extreme difficulty arising 
from the large number, their small size, and the closeness with which 
they are generally crowded together. The number however I believe 
lies between 26 and 32 in the spermatogone: 16 and 18 in the 
spermatocyte; and either 8 or 9 in the spermatid and spermatozoon. 
These are the conclusions drawn from careful counting in a very 
large number of cases. 
In the nucleus of the spermatogone and spermatocyte, double 
staining with safranin and dahlia shows besides the nuclein (chromatin) 
