Evidence from Metazoan Gcrm-Cclh 7 



anterior and a posterior }3ortion. The posterior portion becomes 

 the anniilus {an., figure .S(j) while tlie anterior one divides again, 

 forming the Xoduli i)osteriores" * (g-P-, figure 'Ui). Throughout 

 their career these bodies or granules are highly stainable with 

 certain dye-stuffs. 



Out of the idiosome (S, figure ti7) which as a rule is a body 

 "fiir sich" — in itself alone — develops the ])erforat()riuni. or lnad 

 cap of the adult sperm {li.c, figure 3()). It is agreed that the 

 mitochondria {Jf, figure 37) in the spermatids of many animals, 

 particularly of many vertebrates "furnish the material" ^ 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 graTiulcs sur- 

 rounding the axial filament in the connecting piece, l^ut while 

 the connecting piece of the Seal sperm seems not to be tyi)ical 

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

 tube, or "manchette" of some authors, in a form which is s])ecially 

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

 ture is a thin sheath enveloping the cytoplasmic ])art 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 a))pears 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 exam|)le. 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 es])rcially 

 favorable for observation. "It may be reajclily 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 

 fells us that her study of the develo])ment 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 cj^toplasm surrounding the axial thread a series 



