MUSEUM OF COMPARATIVE ZOOLOGY. 503 



spermatozoon falls pre-eminently the function of fecundation, other sper- 

 matozoa may participate in the act through the active intervention of 

 this protuberance of hyaline protoplasm. 



To explain these phenomena the authors assume that a body (Eikern) 

 in the yolk, which at the approach of spermatozoa enters upon a state of 

 activity, exercises an attraction both on the protoplasm of the yolk and 

 on the spermatozoa, which diminishes with the distance, but increases 

 with the mass, and that this body is movable in the yolk. The radially 

 arranged spermatozoa at the surface of the " watch-glass " give the im- 

 petus to a change in the nearest protoplasm of the egg, by means of 

 which the [egg] nucleus is formed. The first effect is the detachment 

 of the protoplasm from the " watch-glass," and the attraction of that 

 spermatozoon which meets with the least resistance. Since the attraction 

 of yolk and nucleus is to be considered as mutual, and as proportional 

 to the mass, and since the greater part of the egg lies on the side of the 

 eccentric nucleus toward the passive pole, it follows that the yolk will 

 xjommunicate to the nucleus a motion toward its (yolk's) centre. The 

 nucleus thus becomes further removed from the " watch-glass," and its 

 attractive influence on spermatozoa diminishes. Therefore any sperma- 

 tozoon which might chance to follow the same (microyplar) radius as 

 the first one would be less strongly attracted, and thus may be explained 

 why as a rule only one spermatozoon passes the membrane through the 

 micropyle. 



From the nature of their fertilization it was not possible for Whitman 

 iC78") * to observe the penetration of spermatozoa into the eggs of Clep- 

 sine. A nuclear body, which he from analogy cqncludes is the male 

 pronucleus, makes its appearance usually about the time the second 

 polar globule is formed. It has also been detected before the formation 

 •of the firs.t polar globule. It is found near the centre of the egg before 

 the female pronucleus has receded much from the oral pole. The nature 

 of these pronuclei will be discussed farther on. During the formation, 

 or at least during the migration and conjugation of the pronuclei, re- 

 markable changes occur at the poles of the egg, which previous observers 

 had seen only from the surface and designated as "polar rings." By 

 means of sections Whitmah was enabled to study the internal changes 

 which the substance of these rings undergoes. 



About fifteen minutes after the second polar globule is formed a trans- 

 parent fluid substance begins to collect in a shallow groove which en- 

 oircles the oral (animal) pole, thus forming the first polar ring. At 



* See also Whitman '79. 



