118 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



the backward migration of the distal centrosome. In that case this body 

 would correspond to the extra-nuclear centrosome in Scolopendra. 



E. Acrosome. 



In recent years the origin of the body forming the apex or perforating 

 part of the spermatozoon — named by von Lenhossek ('98) the acrosome 

 — has been made out in a number of animals representing diverse groups. 

 It has been shown that in many if not all cases it arises from some por- 

 tion of the archoplastn. In insects Platner ('89) describes the acrosome 

 as being formed from the centrosome. The later works by Henking 

 ('91), Wilcox ('96), Paulmrcr ('99), and Meves (:00), however, show 

 conclusively, I think, that Platner was in error, and that the acrosome 

 arises either from a constricted-off portion of the Nebenkern or from a 

 structure coexistent with this and having a similar origin from some por- 

 tion of the archoplasm. 



The results in the case of vertebrate material have been quite similar. 

 In the elasmobranchs Moore ('95) has ascribed an archoplasmic origin 

 to the acrosome; while in the Amphibia, Meves ('97) and McGregor 

 ('99) respectively conclude that it is formed either from the entire idio- 

 some or from a portion thereof. Niessing (:96) states that in mammals 

 the centrosome is contained in the acrosome; but that this conclusion is 

 erroneous is shown by the later work of von Lenhossek ('98) and Meves 

 ('98, '99). Von Lenhossek derives the acrosome from the cytoplasm, 

 while Meves shows that both in the rat and guinea pig it is produced 

 directly by a metamorphosis of the idiosome. 



Concerning the formation of the acrosome in Lithobius, Tbnniges says, 

 "Die Splmre, welche ursprunglich mit den Centrosomen in Verbindung 

 stand und sodann den Zusammenhang mit ihnen verlor, legt sich dem 

 Kern an und bleibt nunmehr dicht an ihm liegen." A vacuole appears 

 within it, when the axial filament unites with the nucleus, and later its 

 substance is condensed into a deeply staining corpuscle, the apical piece, 

 " welches mit der Spitze des zum Kopf gewordenen Kerns mittelst eines 

 kurzen Stiels in Verbindung steht." In connection with this corpuscle 

 there appears a deeply staining substance which covers the anterior end 

 of the nucleus in the form of a thin cap. From the figures of Tonniges 

 it appears to me that the body seen at one side of the nucleus at early 

 stages, which he has interpreted as the sphere, in reality corresponds to 

 the extruded karolymph observed in the corresponding stage of Scolo- 

 pendra. (Compare my Figures 80, 81, with Figure 316, A, of Tonniges.) 



