GROWTH AND DIFFERENTIATION OF THE GERM-CELLS 163 



of fertilization would lead us to expect, the centrosome of the sper- 

 matid passes into the middle-piece. 



Accounts vary considerably regarding the origin of the acrosome, 

 which according to most authors is of cytoplasmic origin, while a few 

 describe it as arising inside or from the anterior part of the nucleus. 



{b) Composition of the Spcrniatid. — The confusion that has arisen 

 in this difficult subject is owing to the fact that the spermatid may 

 contain, besides the nucleus and centrosome, no less than three addi- 

 tional bodies, which were endlessly confused in the earlier studies 

 on the subject. These are the NcbcJikcni} the attraction-sphere or 

 idiosome (MLtv&s), and the cl/roi/iatoid Xcbaikorpcr {"R^nd^.). 



The Nebenkern (Fig. 82), first described by Biitschli {'■ji)'m the 

 spermatids of butterflies, was afterward shown by La Valette ('86), 

 Platner (^^6, '89), and many later investigators to arise wholly or in 

 part from the rcjjiaijis of tJic spindle of the second spermatocyte 

 division. Its origin is thus related to that of an attraction-sphere 

 (which it often closely simulates), since the latter likewise arises 

 from the achromatic figure. To the remains of the spindle, however, 

 may be added granular elements, probably forming reserve-material 

 ("centro-deutoplasm of Erlanger), that are scattered through the cyto- 

 plasm or aggregated about the equator of the spindle (Fig. 126). 

 Thus the Nebenkern may have a double origin, though its basis is 

 formed by the spindle-remains. The Nebenkern sometimes takes a 

 definite part in the formation of the tail-envelopes and of the acro- 

 some (insects), but in many cases it seems to be wholly wanting.^ 

 The idiozome is in some cases an undoubted attraction-sphere derived 

 from the aster of the last division and at first containing the centro- 

 some, e.g. in the earthworm as shown by Calkins ('95) and Er- 

 langer ('96, 4), in the salamander and guinea-pig, Meves ('96, '99), 

 and in Helix according to Korff ('99), though in later stages the 

 centrosomes usually pass out of the body of the idiozome. In some 

 cases, however (in the rat, according to Lenhossek, '99), the idiozome 

 seems to arise independently through condensation of the cytoplasmic 

 substance into a sphere having no relation to the centrosomes. In 

 some cases the idiozomes of adjoining cells remain for a time con- 

 nected by bridges of material (Fig. 7) representing the remains of 

 the spindle, and hence corresponding to a Nebenkern {e.g. salaman- 

 der, Meves, '96), and the distinction between Nebenkern and idio- 

 zome here fades away. The idiozome is usually concerned in the 

 formation of the acrosome (Amphibia, mammals), but sometimes seems 



' The English equivalent of this should be paranucleus, but the latter word has already 

 been used in various other senses, anil it seems preferaVjle to retain Biitschli's original Ger- 

 man word. 



^ For critical discussion, see Erlanger, '97, I. 



