644 LECTURE XXIV. 



universal and important in the operations of the living animal, ceases 

 to wear the aspect of exaggeration. 



It is, however, certain that the most extraordinary consequences of 

 the fissiparous property of the nucleated cell are unknown in the 

 Yertebrated classes, of which generation without fecundation of the 

 procreating individual is an example. This phenomenon, which at 

 first so much astonished and perplexed physiologists, as observed 

 only in the Aphides, becomes inteUigible and reducible to general 

 law, and is extensively manifested in the Invertebrate series of 

 animals. 



The Monad divides itself before our eyes, constituting two, then 

 four, next eight individuals, and so on. The impregnated germinal 

 vesicle, which the Monad permanently represents in nature, propa- 

 gates, in like manner, by spontaneous fission and assimilation, a number 

 of impregnated cells like itself. Most of these cells are metamor- 

 phosed into the tissues of the growing embryo, but not necessarily all. 

 Certain nucleated cells, the progeny of the primordial one, and in- 

 heriting its powers, may become, without further stimulus, the centres 

 of development of processes like those which have built up the body 

 that contains them : they may bud forth from the stem of the Hydra, 

 and form new individuals by the process of gemmation ; they may bud 

 forth, in like manner, from the larval polype of the Medusa, which 

 thereby procreates in its immature, and, as it seems, virgin state, like 

 the wingless larvae of the summer Aphides ; they may enter the 

 unimpregnated oviducts of these insects, and be there developed in 

 the manner which has already been described.* 



Did time permit, I might easily multiply the instances from the 

 Invertebrate organisations, which bear directly on the establishment of 

 the most important general laws in physiology. I shall conclude by 

 adverting to one which is alike interesting to the anatomist and natu- 

 ralist, and which has exercised the powers of the most active and 

 enquiring intellects of the present age. To the disquisitions and 

 discussions in which Goethe, Oken, Cuvier, and Geoff'roy have 

 taken part, the doctrines of Morphology and of Unity of Organisation 

 owe their existence. 



Some of the medical acquaintances of John Hunter, who, we are 

 told, complacently apostrophised his pursuits in the language of pity, 

 when they found him dissecting a snail, a bee, or a worm, little 

 dreamt of the expanded views of the animal organisation at w^iicli he 

 w^as obtaining glimpses through those narrow casements. It would 

 seem that Hunter himself was oppressed with the vastness of the 

 prospect, w^th the grandeur of the generalisations which his investi- 



* Lecture XVIEI. Inskcta, p. 387. 



