88 Don W. Fawcett and Mario H. Burgos 



Formation of the acrosome and head cap 



The large juxtanuclear body of the spermatid which is 

 commonly referred to as the idiosome-Golgi complex, appears 

 under the electron microscope as an aggregation of minute 

 vacuoles and broad, flattened vesicles (Figs. 2 and 3). The 

 latter are often closely approximated in parallel array and 

 hence, in section, have a lamellar appearance. The small 

 vacuoles seem to arise by being budded off from the edges of 

 the flattened vesicles. With cytological staining methods, the 

 parallel arrays of membranes are apparently impregnated 

 more heavily with osmium or silver than is the rest of the 

 complex and they are identified with the light microscope 

 as rod-like or crescent-shaped Golgi bodies (dictyosomes). 

 The masses of minute vacuoles, staining less heavily, have been 

 designated the idiosomal material (archoplasm). Inasmuch as 

 the Golgi complex in all other cell types examined to date also 

 contains both the minute vacuoles and the parallel arrange- 

 ments of membrane-bounded vesicles, there appears to be no 

 reason for retaining, in the case of the spermatid, the special 

 terms "idiosome", "archoplasm" or "sphere" for a part of 

 this structure. Instead, the whole body is to be regarded as a 

 particularly well-developed Golgi complex, differing in no 

 essential respect from that of other cell types. 



Early in the differentiation of the spermatid one or two 

 large granules are formed within separate vacuoles of the 

 Golgi complex. These proacrosomal granules are moderately 

 dense to electrons and are generally homogeneous with present 

 resolutions. Coalescence of the vacuoles, and of the granules 

 which they contain, results in the formation of a single 

 sizeable acrosomal granule within a rather large acrosomal 

 vesicle. The latter is bounded by a distinct membrane and, 

 in life, probably has a fluid content but this is represented in 

 the electron micrographs only by a faint, flocculent precipitate 

 seen in the vacuole around the acrosomal granule (Fig. 3). 

 The acrosomal vesicle approaches the nucleus and adheres 

 to its anterior pole and at the same time the granule in its 



