INSECTA. 233 



extremities has proceeded to the formation of obscure joints and 

 terminal hooks. The rudimental palpi begin to bud from tlie maxillsB 

 and labium ; the mandibles acquire their hard terminal hooks, and 

 closely resemble the thoracic feet. In this state the larva is excluded- 



At an earlier period the simple bulbous antennae, mandibles, and 

 maxillae, indicate three cephalic segments, equal in size and distinct- 

 ness to those of the thorax. The labrum and labium might perhaps 

 be regarded as indicative of two other abortive segments, but with 

 this concession not more than five cephalic segments can be defined 

 by observation of the early development of the insect. The biliary 

 and other tubular glands result from juxtaposition in a linear series 

 of vitelline nucleated cells, which coalesce by liquefaction of the 

 parts of the capsule in contact with each other, the nuclei remaining 

 longer and indicating the primitive separation of the cells. The 

 ovarian tubes have appeared to me, in the larva of the silkworm, to 

 retain the primitive series of nucleated cells at their capillary begin- 

 nings without coalescence, which has taken place to form the lower 

 part of the tube: such persistent, primitive, nucleated granules seem 

 to form the basis for the formation, by the usual fissiparous multipli- 

 cation^ of the subsequent ova. 



In the Aphides the corresponding vitelline cells retain their share 

 of the fecundating principle (which was diffused through the pa- 

 rent egg by the alternating fissiparous, liquefactive and assimilative 

 processes,) in so potent a degree, that a certain growth and nutritive 

 vigour in the insect suffice to set on foot, in the ovarian nucleated 

 cells, a repetition of the fissiparous and assimilative processes by 

 which they transform themselves in their turn into productive insects ; 

 and the fecundating force is not exhausted by such successive sub- 

 divisions, until a seventh, a ninth, or an eleventh generation. 



This procreation from a virgin mother, this transmission of the 

 virtue of the ancestral coitus to the ninth generation, have hitherto 

 ranked amongst the most marvellous and inexplicable phenomena in 

 physiology. Reaumur eluded the difficulty by affirming the Aphides 

 to be androgynous; but all subsequent entomologists deny the ex- 

 istence of any trace of male organs in the virgin larviparous Aphis ; 

 and all have recognized the distinct winged male insect. Leon 

 Dufour referred the phenomena to spontaneous or equivocal genera- 

 tion, which is independent of any impregnation. But this kind of 

 generation is purely hypothetical, and has been rendered less and 

 less probable by every successive exact observation and experiment; 

 and in the Aphides the male insects are unequivocal and numerous. 



Professor Morren, the latest and most exact observer of the anatomy 

 and habits of the Ajjludes, alludes to an opinion he had formerly lield. 



