According to Balbiani, the elements that cover the interior of the tubuli semin:feri form four concentric zones: 1st. A layer of flattened polygonal cells, which are regular and applied directly to the wall of the tube.
2d. A layer of small round and granular cells.
3d. A layer of large round or pyriform cells.
4th. A zone of fascia of spermatozoids, which are free within the middle of the tube, and which are placed in radiating lines. .
The small cells first appear as buds in the large polygonal cells, and as soon as some cells are thus developed, others proceed from the first by segmentation, and there are thus formed groups of cells, more or less numerous, and always connected by their prolongations to the mother cell. Then the pedicles lengthen, the cells increase in volume, and it is thus that the groups of large, round cells are formed. Finally, when these latter have arrived at a certain degree of development, the mother cell, or polygonal cell, sends out its prolongation in the shape of a small column; the groups of spermatoblasts are thus lifted up, and taken towards the lumen of the c,analicule.
Finally, according to Duval, the spermatozoid develops in the following manner: There develops in the spermatoblasts a globule of an homogeneous aspect, which is highly refractive and colored carmine. It is entirely independent of the nucleus, and is situated in the pellicle which unites, in the shape of a racket, the spermatoblasts to the mother-cell. At first, it is entirely enveloped in the protoplasm, but later, it escapes, becomes free, and, at the same time, is transformed into the head of the spermato zoid. At the same time that the head forms, the caudal filament appears at the other pole of the spermatoblasts in the protoplasm. This soon lengthens and emerges from the cell.
The middle segment also develops by differentiation of the protoplasm.
At the free extremity of the lengthened spermatoblasts, which are now provided with their nuclei, there forms a pencil of vibratile cilite, which penetrates the cellular body and there terminates in a slight enlargement.
In his researches on spermatogenesis of the Batrachians, Duval has estab lished that, in the red frogs, where the development of the spermatic elements can be followed from their origin to their complete formation, this development must be watched for more than eighteen months to note all the phases.
" If we examine the section of a seminiferous tube in the month of November, for instance, we find, with little magnifying, that this section (Fig. 69) forms an elegant design made by the fascia of spermatozoids (FS and fs), which are regularly placed like the spokes of a wheel. That is, the pencils formed by the caudal filaments (fs) point towards the centre of the canalicule, the lumen of which they almost completely fill, leaving only a small central space free (A), which is surrounded by these pencils, more or less distinctly separated from each other. The shorter and more distinctly marked fascia (FS), formed by the heads of these same spermatozoids, point towards the wall of the canalicule in which they seem implanted in the midst of a granular mass (G) strewn within nuclei easily seen with a higher power.
"At a power of from 320 to 400 diameters, the details of this implanta tion are seen to be as follows: The corresponding extremity of the fascia, formed by the heads of the spermatozoids, is continued by a band of granular matter which adheres to the wall of the canal. At the sides of this band, and on the walls of the canal, are anatomical elements, some in the shape of nuclei, others as cells. The first we will call granular cells, the second are the male ova. By comparing the different forms of granular cells and male ova, we find a series of forms intermediate be tween the granular cells and the male ova.
" That is, these last are only a transformation, a more advanced state of the former.
" If we begin our study with these elements, we will have to examine what becomes of, first, the fascia of the spermatozoids, and secondly the granular cells and male ova.
"The fascia of the spermatozoids separate,towards the end of November, little by little from the wall, lose all connection with it, become free, and in February, and the beginning of March, they enter the excretory canals. (Figs. 70 and 71.) "As for the granular cells and male ova, we will see, during this same period, the multiplication of the granular cells, their evolution into male ova, then, after this period, the transformation of the male ova into large cells with many nuclei, which are themselves transformed, during a second period, after March, and during the whole of spring and summer, into fascia of spermatozoids.