THEIR SIGNIFICANCE IN HEREDITY. 349 



idea, referring- to my observations and also to a new discovery of 

 his own. In a recent number of the ' Biologische Centralblatt,' 

 Blochmann * gives an account of his continued observations upon 

 the formation of polar bodies. It is well known that this careful 

 observer had previously shown that polar bodies do occur in the 

 eggs of insects, although they had not been found before. Bloch- 

 mann proved that they are found in the representatives of three 

 different orders, so that we may indeed ' confidently hope to find 

 corresponding phenomena in other insects.' This discovery is 

 most important, and it was naturally very welcome to me, as I 

 had for a long time ascribed a high physiological importance 

 to the process of the formation of polar bodies, and it would not 

 be in accordance with such a view if the process was entirely 

 wanting from whole classes of animals. To fill up this gap in 

 our knowledge, and to give the required support to my theoretical 

 views, I had proposed to one of my pupils, Dr. Stuhlmann 2 , that 

 he should work, out the maturation of the eggs of insects ; and it 

 is a curious ill-luck that he, like many other observers, did not 

 succeed in observing the expected expulsion of polar bodies, in 

 spite of the great trouble he had taken. It may be that the 

 species selected for investigation were unfavourable : at all events, 

 we cannot now doubt that a division of the egg-nucleus is 

 quite universal among insects, for Blochmann, in his latest con- 

 tribution to the subject, proves that the Aphidae also form polar 

 bodies. He examined the winter-eggs of Aphis aceris, and as- 

 certained that they form two polar bodies, one after the other. 

 Even in the viviparous Aphidae, thin sections revealed the presence 

 of a polar body, though Blochmann could not trace all the stages 

 of its development. It appears that the polar body is here pre- 

 served for an exceptional period, and its presence can still be 

 proved when the blastoderm has been formed, and sometimes 

 when development is even further advanced. Skilled observers of 

 recent times, such as Will and Witlaczil, have not been able to 

 find a polar body in the parthenogenetic eggs of the Aphidae, and 



1 Blochmann, 'Ueber die Kichtungskorper bei den Insekteneiern,' Biolog. Cen- 

 tralblatt., April 15, 1887. 



2 F. Stuhlmann, 'Die Reifung des Arthropodeneies nach Beobachtungen an 

 Insekten, Spinnen, Myriapoden und Peripatus,' Berichte der naturforschenden 

 Gesellschaft zu Freiburg i. Br., Bd. I. p. 101. 



