Katharine Foot and Ella Church Strobell 323 



phologically alike, it would be convenient to designate them as the 

 ojiierior and posterior male asters — and it is impossible to resist an at- 

 tempt to homologize them to similar structures described for other 

 eggs — although we appreciate the danger of making too rigid an appli- 

 cation of the phenomena observed in individual cases. 



Lillie (10) in his suggestive work on Unio describes two asters, the 

 first, which he identifies as the true sperm attraction-sphere, appears 

 and disappears at about the same stage of the egg's development, as the 

 anterior sperm aster (the cone) of AUolobophora; while the second, his 

 "accessory aster," appears and disappears at about the same period as the 

 posterior sperm aster of Allolohophora. It is significant, that the sperm 

 aster of Unio is " comet shaped," thus resembling the fertilization cone 

 of AUololopliora, and it is also significant that it is found, sometimes 

 preceding the head of the sperm. Is it not possible that the male 

 aster and accessory aster of Unio correspond to the anterior and posterior 

 sperm asters of AUololopliora, the approxiinate agreement in the time of 

 their appearance and disappearance being due to the fact that both 

 eggs are fertilized at about the same stage of development ? 



'In Axolotl, Fick (2) figures a distinct spherical body at the base of 

 the spine of the spermatozoon, although he does not call it a centrosome. 

 In the egg he sees a cytoplasmic reaction to the head of the spermato- 

 zoon, the so-called funnel. Fertilization occurs later in this egg, than 

 is the case in AUololopliora — and yet the funnel and the sperm aster of 

 Axolotl are undoubtedly homologous to the anterior and posterior sperm 

 asters of AUololopliora. 



In the egg of Allolohophora fertilization occurs very early, this fact 

 marking the individuality of these two structures, the anterior male 

 aster (the cone) appearing at the metaphase of the first maturation 

 spindle, and the posterior male aster, after the first polar body is formed 

 — thus separating the two structures by a period of time as well as posi- 

 tion. In eggs in which fertilization takes place later, the cytoplasmic 

 reactions to the spine and middle-piece following each other very rapidly, 

 is it not possible that in some cases the anterior and posterior male asters 

 may be fused or confused ? 



If we call in evidence the data indicating that division is one of the 

 life expressions of the centrosome, and if we interpret the three small 

 bodies in the spermatozoon of AUololopliora as centrosomes, it involves 

 the unauthorized assumption that the centrosome of the spermatid di- 

 vides, part being destined to the apex of the head and part for the 

 middle-piece of the spermatozoon, these centrosomes being the equiva- 

 lent of the one centrosome left in the egg after the formation of the 



