BEPRODUCTIVE ORQAXS. 95 



individuals into communities the so-called animal-polities which 

 may be complicated by the division of labour (Bees, Wasps, Ants, 

 Termites). 



In fact here the combined action appears to be mutually assisting 

 or mutually limiting, as we find in the so-called animal stock?, 

 the individuals of which are bound together by continuity of 

 body. The advantages to be gained by this mutual rendering of 

 service are not merely limited to the greater facilities for nourish- 

 ment and defence, and therefore for the preservation of the in- 

 dividual ; but, above all, tend to the maintenance of the offspring, 

 and hence to the preservation of the species. It is for this reason 

 that the simplest and commonest associations, from which the more 

 complicated communities, subdivided by partition of labour, are 

 derived, are generally communities of both sexes of the same 

 species. 



REPRODUCTIVE ORGANS. 



On account of the limit set to the duration of the life of every organ- 

 ism, it appears absolutely necessary for the preservation of the animal 

 and vegetable kingdoms that new life should originate. The forma- 

 tion of new organisms might be due to spontaneous generation 

 (yeneratio equivoca) ; and formerly this was supposed to take place, 

 not only in the simpler and lower organisms, but also in the more 

 complicated and higher. Aristotle thought that Frogs and Eels arose 

 spontaneously from slime ; and the appearance of maggots in putre- 

 fying meat was, till Redi's time, explained in the same manner. 

 With the progress of science the limits within which this supposition 

 could be applied became ever narrower, so that they soon came to 

 include only the Entozoa and small animals found in infusions. 

 Finally it has been shown by the researches of late years that these 

 organisms also must, for the most part, be withdrawn from the region 

 of the yeneratio equivoca ; so that at present, when the question of 

 spontaneous generation is discussed, it is only the lowest organisms, 

 those found in putrefying infusions, that are considered. The 

 greater number of investigators,* supported by the results of 



* Cf. especially Pasteur, " Memoire sur les corpuscules organises qui existent 

 dans 1'atmosphere " (Ann. des. Sc. Nat.), 1861 ; also " Experiences relatives 

 amx generations dites spontanees '' (Compt. rend, de 1'Acad. des Sciences, 

 tome 50). 



