212 Papers from the Marine Biological Laboratory at Tortugas. 



treatment of the tissue may be eliminated. However, it leaves great gaps 

 in the stages of development of the apyrene spermatozoa and affords very 

 little or no chance of determining the finer details of the protoplasmic 

 differentiations and the structural changes that occur in the cell. For this 

 purpose the study of material that has been well fixed and stained is alone 

 available. 



GROWTH OF THE APYRENE SPERMATOBLAST. 



In Strombus the large nucleated cell which becomes differentiated into 

 the apyrene spermatosome can be traced back through a period of unin- 

 terrupted growth to a small cell, the apyrene spermatoblast, which is 

 distinct from either the eupyrene spermatocytes or spermatogonia. This 

 cell (fig. 8) lies close to the walls of the lobules of the testis and may be 

 surrounded by older cells of the same nature or by the general syncytium 

 of the testis or partially by both. Two or three of these cells, lying in the 

 syncytium and isolated from others of their kind, are frequently in close 

 proximity to a nest of eupyiene spermatogonia and would be taken at 

 first glance to belong to that nest. Closer and more careful examination, 

 however, reveals certain distinct, if minute, differences between them and 

 the spermatogonia. 



In the first place, there is a difference of position. Where they occur, 

 the young apyrene spermatoblasts always lie between the wall of the lobule 

 and the spermatogonia. If the group of apyrene spermatoblasts is a larger 

 one, it is seen that the outer cells are larger and older than those lying next 

 to the wall of the lobule. Such a group as that may be surrounded by 

 several nests of spermatogonia or by spermatocytes. A comparison of all 

 the nuclei of all these various cells shows that those of the outer spermato- 

 blasts are as large or larger than the spermatogonial nuclei, while those of 

 the inner spermatoblasts are smaller. But the cytoplasmic bodies of even 

 the youngest spermatoblasts are larger than those of the spermatogonia and 

 they are inclosed by definite membranes. The cytoplasm of the spermato- 

 gonia forms a thin sheath around their nuclei and the cell-walls are so 

 delicate that very often it is impossible to distinguish them in the cytoplasm 

 of the surrounding syncytium. 



The nuclei of the apyrene spermatoblasts and of the eupyrene spermato- 

 gonia differ in pattern. In the latter, during the resting stages, the chro- 

 matin forms an irregular and dense network, the strands of which show many 

 free ends and, when seen in cross-section, have very frequently the appear- 

 ance of granules. Once the spermatogonia have begun to grow, the nuclear 

 pattern changes gradually until the typical spireme of the spermatocyte is 

 formed. The nuclear pattern of the spermatoblasts, on the other hand, 

 remains constant until a late period in the growth of these cells, when they 

 can be easily distinguished from the eupyrene cells by their increased size. 

 These nuclei are relatively rich in nuclear sap and poor in chromatin, the 

 latter being present in the form of irregular granules which are partially con- 

 nected by a chromatic material (figs. 8-14). At least one karyosome is 

 always present in the nucleus. 



