MATURATION AND IMPREGNATION OF THE OVUM. 123 



way, the process of regeneration of the germinal vesicle. Views 

 analogous to this are held by Strasburger and Hertwig, who 

 regard the formation of the polar bodies in the light of a process 

 of excretion or removal of useless material. Such hypotheses 

 do not unfortunately carry us very far. 



I would suggest that in the formation of the polar cells 

 part of the constituents of the germinal vesicle which are requisite 

 for its functions as a complete and independent nucleus are 

 removed to make room for the supply of the necessary parts to 

 it again by the spermatic nucleus {videTp. 126). More light on this, 

 as on other points, may probably be thrown by further investiga- 

 tions on parthenogenesis and the presence or absence of a polar 

 cell in eggs which develope parthenogenetically. Curiously 

 enough the two groups in which parthenogenesis most frequently 

 occurs in the ordinary course of development [Arthropoda and Boti- 

 fera) are also those in which polar cells, with the possible exception 

 mentioned above, of the parthenogenetic eggs of Lacenularia, are 

 stated to be absent. This curious coincidence, should it be con- 

 firmed, may perhaps be explained on the hypothesis, I have just sug- 

 gested, viz. that a more or less essential part of the nucleus is re- 

 moved in the formation of the polar cells ; so that in cases, e.g. 

 Arthropoda and Rofifera, ivhere p)olar cells are not formed, and an 

 essential part of the nucleus not therefore removed, parthenoge- 

 nesis can much more easily occur than tvhen polar cells are formed. 



That the part removed in the formation of the polar cells is 

 jiot absolutely essential, seems at first sight to follow from the 

 fact of parthenogenesis being possible in instances where impreg- 

 nation is the normal occurrence. The genuineness of all the 

 observations on this head is too long a subject to enter into here,^ 

 but after admitting, as we probably must, that there are genuine 

 cases of parthenogenesis, it cannot be taken for granted without 

 more extended observation that the occurrence of development 

 in these rare instances may not be due to the polar cells not having 

 been formed as usual, and that when the polar cells are formed 

 the development without impregnation is less possible. 



The remarkable observations of Professor Greeff (19) on 

 the parthenogenetic development of the eggs of Asterias 

 ruhens tell, however, very strongly against this explanation. 

 Greeff has found that under normal circumstances the eggs of this 



1 The instances quoted by Siebold from Hensen and Oellacher are not 

 quite satisfactory. In Hensen's case impregnation would have been possible 

 if we can suppose the spermatozoa to be capable of passing into the body- 

 cavity through the open end of the uninjured oviduct ; and though Oella- 

 cher's instances are more valuable, yet sufBcient care seems hardly to have 

 been taken, especially when it is not certain for what length of time 

 spermatozoa may be able to live in the oviduct. For Oellacher's precau- 

 tions, vide 'Zeit. fiir Wiss, Zuol.,' Bd. xxii, p. 202. 



