Transmission electron micrograph of the implantation fossa, centriolar adjunct, and base of the flagellum in a chinchilla spermatid. The juxtanuclear proximal centriole, visible at the arrow, is continuous with the centriolar adjunct. The cavity of the centriolar adjunct is narrower than that of the centriole proper. The transverse section at lower left corresponds to the white line in the upper figure, and shows the pinwheel of microtubule triplets. The transverse section at lower right, corresponding to the black line in the upper figure, illustrates the relative narrowness of the adjunct and shows other structural differences between the centriole and its adjunct.