The mature spermatozoon consists: (1) of a sharp, spear-like point; (2) a tube-like head about .02 mm. long, composed of a densely staining outer wall and a clearer central cavity; and (3) a filamentous tail about .5 mm. long. The point comes from the acrosome, the head from the nucleus, and the tail from the axial filament and nebenkern. While I do not deny the presence of a middle piece, my observations do not warrant me in describing one, although fig. 40 would suggest it.
Dr. R. von Erlanger (’97, 1, and ’97, 2) and Dr. F. Meves (’00) have given excellent discussions of the literature on the nebenkern. I cannot do better than direct the attention of other investigators to them. Hence, I shall discuss only such authors and such points as have special bearing on my own results. The spermatid changes in the Gryllidæ have been studied, so far as I know, only by St. George (’67) and by vom Rath (’92).
St. George, in his early paper, described the transformation process in the “Hausgrille” along with other insects. He found the “Nebenkörper,” and saw that it took a part in forming the envelope of the axial filament, a small particle remaining near the nucleus and other drops of it appearing at intervals on the tail. In his paper on _Blatta_ (’86, 1) he accepted Bütchli’s name, “nebenkern,” and traced its origin to the spindle remains. In his paper on _Phratora_ (’86, 2) he takes up the description of the nebenkern in the spermatocytes and spermatogonia. In the spermatid, he describes the blackberry stage in these words: “Während das andere (not nucleus) Körperchen weniger lebhaft gefärbt als ein kleiner Fadenknäuel mit unregelmässigem Contour erscheint.”
There can be no true nebenkern in the spermatogonia and spermatocytes, as St. George first used the word, and as I have limited its application. But St. George found the object, traced its origin and fate, and described several of the stages as they appear in _Gryllus_.
Vom Rath (’92) found _Gryllotalpa_ very poor material for following the spermatid changes. However, he described an oval body which he found varied in appearance, depending on the method of fixation. He calls it the “nebenkern” and thinks it goes to help form the tail.