'PHYSIOLOGICAL UNITS' 85 



experiments are equivocal because bastard larvae, arising by the 

 union of an entire egg with the spermatozoon of a distinct species, 

 may also present the pure paternal form. At the same time, 

 referring to the criticism raised by Pfeffer and others, that the 

 spermatozoon is an entire cell and not merely a nucleus, he points 

 out that this argument is not admissible in appraising the part 

 played by the egg protoplasm in fertilisation. In bastard larvae 

 which have obtained nuclear substance only from the spermatozoon, 

 in the fertilisation of egg fragments without nucleus (' merogonie '), 

 the paternal type appears exclusively." 



It certainly seems that in these experiments there is no positive 

 evidence that the fragment of denucleated egg has communicated 

 any of its female traits to the bastard offspring, although it has 

 served as a matrix in, and with the aid of which (as mere nutritive 

 material), the spermatozoon has been capable of giving rise to a 

 larva of its own type. This must be regarded as a truly wonderful 

 result, of a kind never before known : though it seems to be the 

 converse of a class of facts hitherto well known, in which the eggs 

 of certain animals are capable of going through all their phases 

 of development altogether independently of contact and fusion 

 with a spermatozoon. 



This so-called ' parthenogenesis ' or ' virgin reproduction ' is now 

 well known to be by no means a rare phenomenon. As Weismann 

 says, " It occurs regularly and normally in many cases, especially 

 in the very diverse groups of the great series of Arthropoda. 

 Thus among insects it is found in certain saw-flies, gall-flies, 

 ichneumon-flies, in the honey bee, and in common wasps, and 

 it is particularly wide-spread among plant-lice (Aphides) such as 

 the vine-aphis (Phylloxera), whose prodigious multiplication in a 

 short time depends partly on the fact that all the generations with 

 the exception of one, consist only of females with a parthogenetic 

 mode of reproduction. Among the lower Crustaceans also par- 

 thenogenesis plays a large role, and in many species it even 

 occurs as the sole mode of reproduction, but more often — as is 

 also the case among insects — it occurs alternately with bi-sexual 

 reproduction" {loc. cit. p. 303). 



There is a very interesting point in connection with this occur- 

 rence of 'parthenogenesis,' and its relation to what occurs in 

 ordinary bi-sexual reproduction. It is well known that the egg 

 nucleus previous to fertilisation undergoes what are known as 

 ' reducing divisions ' (leading to the extrusion of the two 



