o/ the Vital and Physical Forces. 375 



are aquatic, it is clear that although pairing takes place at but little 

 above the temperature of freezing, the ova are deposited at a time 

 when diurnal warmth is increasing, because accessions of force 

 from without are necessary to evolve vital force within them, and 

 induce the formation of structure ; and, further, because without 

 these accessions the ova have not within themselves the am_ount 

 of force required and evolved by — and which promotes and sus- 

 tains — the organization of the parent. 



This then appears to be true with regard to all the ovipara : that 

 the ova require increments and alternations of heat-force from 

 without to promote the development of the embryo, although the 

 increment required by some may be slight. The force thus derived 

 from the inorganic world induces changes in the constituents of 

 the ovum, the result of which is the production of vital power. 

 From these constituents, originally an aggregation of nucleated 

 cells, a layer of cells is separated on the surface of the mass, and 

 this becomes the foundation of the future being. The cells of 

 which it is composed are very similar in appearance to others 

 which form the coumion mass, and it is through changes in 

 these that the embryo is formed. I have watched these changes 

 in many Articulata. The ova of one species, the common ear- 

 wig, Forficula, are well fitted to illustrate the view under consi- 

 deration ; and are in fact, with the ova of Meloe, those from which 

 my view was originally in part deduced. The Forficula rarely 

 deposits her eggs at a temperature below 43° F, or 44° F., and, 

 as naturalists are well aware through DeGeer, and as I have con- 

 stantly observed, the female attends to and incubates them during 

 the whole period of their development, turning and removing 

 them from place to place according as the locality may happen 

 to be of the required warmth or degree of moisture. The cells 

 in the embryo or foundation layer of the impregnated egg grow 

 and expand by accessions of heat and moisture, and some of these 

 acquire gravity through the chemical changes promoted by heat, 

 and by endosmosis and assimilation of substance through the 

 shell in a fluid condition, as well as by assimilation of materials 

 from other cells, which, having arrived at maturity are in deca- 

 dence. The cells of the layer then divide, each into two, and these 

 again enlarge in like manner, and thus mutually promote the 

 growth and enlargement of the whole, as well as the enlarge- 

 ment of the entire ovum by their iridividual expansion and in- 

 crease. These changes are accompanied by an evolution of vital 

 force, as motion, in the forming tissue. Heat thus promoting 

 organization through chemical affinity and gravity results as mo- 

 tive force. Motion among individual cells is the invariable ac- 

 companiment of their growth and subdivision, and the reaction 

 of the cells on each other during their changes is the commence- 



