i6$ THE EVOLUTION OF SEX. 



with the assistance of Herr Ischikawa, has verified it in about a dozen 

 species, Lcptodora hyalina, Sida crystallina, Cypris reptans, and other 

 water fleas. Blochmann has also corroborated Weismann's discovery, 

 in his observations on aphides. What theoretical importance Weis- 

 mann attaches to the fact will be immediately noticed.* 



VIII. Theory of Parthenogenesis. — We may begin with 

 Balfour's view of the case, though that of Minot has the priority. 

 " The function of forming polar cells has been acquired by the ovum 

 for the express purpose of preventing parthenogenesis." If they were 

 not formed, parthenogenesis would normally occur. This is expressed 

 in curiously teleological language, but the main idea is clear enough, — 

 the retained polar cells replace the sperm nucleus. It is only necessary 

 to change cells into cell to make it reasonable today. One must not 

 forget, however, that in higher animals, where parthenogenesis is 

 unknown, polar cells have not been found often as yet, nor ever seen 

 in birds and reptiles. And one would fain get further back still, and 

 know why only one polar globule is formed in parthenogenetic ova. 

 " In accordance with Minot' s hypothesis of sexuality, it might be 

 assumed that in parthenogenetic ova the male element was retained, 

 and that the cell remained a true asexual cell, and did not become a 

 sexual element." "Blochmann and Weismann have shown that this 

 is the case, by their discovery that in parthenogenetic ova only one 

 polar globule is formed, while there are always two in ova which are 

 impregnated ; hence it is probable that one polar globule (by 

 hypothesis, male") is retained." . 



Minot' s words are not beyond criticism either, though they are not 

 teleological. An ovum which retains a male element is not happily 

 described as remaining asexual; it would be better to call it a case of 

 intra-cellular hermaphroditism. Nor can it yet be said that there are 

 always two polar globules in ova which are impregnated. The 

 discovery referred to is historically Weismann's, while a corroboration 

 is due to Blochmann. It is more important, however, to notice how 

 Minot cleverly adapts himself, and rightly too, to increased knowledge 

 of the facts. The parthenogenetic ovum only retains one polar globule, 

 — one male element is enough; two would be "polyspermy," which 

 is abhorred. 



There was no fear that Rolph would indulge in teleology, rigid 

 necessitarian as he was. Parthenogenesis of ova was to him the 

 more natural process, the sperm a subsequent importation. "There 

 is for the ovum a certain minimal mass, which must be surpassed it 



* Blochmann, however, claims to have demonstrated the formation of kvo 

 polar bodies in those unfertilized eggs which are to give birth to drones. 



