Evidence from, Metazoan Germ-Cells 7 



anterior and a posterior portion. The -posterior portion becomes 

 the annulus (an., figure 36) while the anterior one divides again, 

 forming the Noduli posteriores" 4 (g.p., figure 36). Throughout 

 their career these bodies or granules are highly stainable with 

 certain dye-stuffs. 



Out of the idiosome (3, figure 37) which as a rule is a body 

 "fiir sich" in itself alone develops the perforatorium, or head 

 cap of the adult sperm (h.c., figure 36). It is agreed that the 

 mitochondria (4, figure 37) in the spermatids of many animals, 

 particularly of many vertebrates "furnish the material" 3 for the 

 spiral found in the connecting piece (c.p., figure 36) of the 

 sperm. Although no spiral is present in the Seal sperm it may 

 be represented, according to Oliver, by numerous granules sur- 

 rounding the axial filament in the connecting piece. But while 

 the connecting piece of the Seal sperm seems not to be typical 

 as regards the spiral, it presents another structure, the caudal 

 tube, or "manchette" of some authors, in a form which is specially 

 instructive from our standpoint. In the adult sperm this struc- 

 ture is a thin sheath enveloping the cytoplasmic part of the con- 

 necting piece and lying in close contact with the persisting cell 

 membrane. The point of special interest about it is that its 

 persistence in the completed sperm of the Seal appears to be 

 exceptional, for it is known to disappear entirely in the course 

 of development of the sperm of several other mammals. It is a 

 transitory or embryonic organ in some species of sperm, but a 

 permanent one in other species, just as gills, for example, are 

 transitory organs in the ontogeny of some species, as a frog, but 

 are permanent in others, as fish, 



The development of the tube in the Seal sperm is especially 

 favorable for observation. "It may be readily followed," writes 

 Oliver, "from its first appearance up to its final incorporation 

 in the connecting piece as a peripheral layer, or sheath." * Here 

 then is a structure having all the essential marks of devel- 

 opment due to heredity and likewise one the "physical basis" of 

 which has been carefully observed. Mentioning a long list of 

 investigators who believe in the "derivation of the caudal tube 

 by a process of cytoplasmic differentiation alone" Miss Oliver 

 tells us that her study of the development of the fur seal sperm 

 is a complete confirmation of this view. As to the very begin- 

 ning of the tube we read: "Shortly after the centrosomes and 

 their tail filament have reached the nuclear membrane there 

 appears in the cytoplasm surrounding the axial thread a series 



