202 PROF. HUXLEY ON THE AGAMIC REPRODUCTION 



this be the case, however, the second hypothesis is excluded, and the third is improbable 

 in itself, and is supported by no evidence. In the absence of such evidence, the marked 

 contrast in size and appearance between the epithelial endoplasts of the penultimate 

 chamber and those of the germ tends to show that the two have no direct relation to one 

 another. 



Those who have followed the details of the development of the pseudovum and its 

 resulting germ, given above, will not fail to admire the clear insight of Morren, when he 

 affirmed that the agamic offspriag of Aphis was developed by " the individualization of a 

 previously organized tissue." A more neat and expressive definition of the process could 

 not be given : and as Morren nowhere entertains the absurd doctrine that an organized 

 tissue must be as complex as "mucous membrane" or "muscular fibre," which has 

 been attributed to him, the criticisms to which his views have been subjected on this 

 ground are sufficiently baseless. No one Avill pretend to deny that the pseudovarium is 

 " organized," nor that the pseudovum is a portion of it which has become "individualized." 

 But I subjoin Morreu's words, that the reader may form his own judgment as to his 

 merits : — 



" A dii'e vrai, je me refuse a emettre une opinion au milieu d'un tel d^dale, et je tiens 

 pour plus philosophique d'avouer son ignorance dans im phenomene oil la nature nous 

 refuse meme I'apparence d'une explication. S'il fallait uue explication a toute force, 

 j'admettrais que la generation se fait ici com me chez quelques entozoaires, ^«r individuali- 

 sation d'un tissu precedemment organise. La generation n'est pas pour cela spontan^e : 

 une generation spontanee doit etre la production d'un etre organise de toutes pieces, 

 lorsque les elemens inorganiques se r6uniront pom- produire un animal, une plante. 

 Cette generation est impossible et n'a jamais lieu. Une generation equivoque est celle ou 

 des tissus organises pr6alablement par un etre deja poui'vu de vie, s'individualisent, c'est a 

 dire, se sejiarent de la masse commune et participent encore, apres cette separation de 

 I'etat djTianiique de la masse, c'est a dii-e, de sa vie, mais a son propre profit. C'est 

 ainsi qu'im tissu produit un entozoaire *. C'est de la vie continuee. Mais supposez 

 que la vie ait assez d'6nergie poiu' imprimer au tissu que s'individualise la forme de 

 I'espece productrice, et vous avez la generation des pucerons. Cette energie se perd 

 au bout de quelques generations, et une nouvelle impulsion devient necessaire, c'est celle 

 du male. 



" VoUa a tout liasard, une hypothfese que dans ma jeunesse j'aurais embrass^e avec 

 plaisii'; mais aujourd'hui je prefere douter: les faits qiie j'ai exposes plus haut valent 

 mieux qu'une theorie." — Morren, sur le Puceron du Pecher, Annales des Sc. Nat. s^rie 2. 

 vi. 1836, p. 90. 



§ 3. Description of the Oviparous Female Aphis and of the Development of 



the Ovum. 



Throughovxt the two months dui'ing which the Ivy-leafed Geranium, on which my 

 viviparous Aphides are living, has been in my possession, neither males nor females have 



* I need hardly remark, that no evidence of the development of Entozoa, in the way supposed by Morren, is in 

 existence. 



