CHARACTERS OF VERTEBRATE ANIMALS. 



11 



embryo and the Invertebrate adult, — it is not with any of the higlier 

 forms of Invertebrata, — with neither the Cephalopod, the Arachni- 

 dan, nor the Insect, — that such organic correspondence is found to 

 exist ; but it is with the lowest forms and simplest beginnings of 

 animal life, — with the infusorial monads. Only, in fact, during that 

 period of the ovum-life of the Vertebrated being, in which the mys- 

 terious properties of the impregnated gea-m-vesicle are diffused and 

 distributed by fissiparous multiplication amongst countless nucleated 

 cells — the progeny of the primary germinal vesicle and coheirs of 



Ova of the Rabbit, at four early stages of development (Barrj')- 



the seminal virtue — do we find such a form and such properties of 

 the Vertebrated animal as justify us in affirming that tliere is " Unity 

 of Organisation" between it and an Invertebrate animal. (Compare 

 fig. 2. with cut 14., p. 24., Lectures on Invertebrata.) 



The next step in the development of the ovum — and it is so speedy 

 a one, that those which precede it long escaped observation — im- 

 presses upon the nascent being its Vertebrated type. Certain nu- 

 cleated cells lose their individuality and powers of propagation ; they 

 coalesce and fill the fine tubes so formed with albumen, as the final 

 act of their assimilative power, and thus become converted into 

 nervous tissue, in the form of a double chord {fig. 3. ch\ which, from 

 its first beginning, marks the dorsal aspect of the 

 embryonic trace: other nucleated cells lay the 

 foundation of the vertebral column {y) around the 

 spinal chord ; others again cliange into the softer 

 tissues, and the rest, circulating with the nutrient 

 fluid, as blood discs, through channels which 

 sketch out the sanguiferous system, maintain life, 

 and furnish materials by their powers of assimi- 

 lation and spontaneous fission to the growing 

 body. * 

 All vertebrated animals, during a greater or less extent of these 

 developmental processes, float in a liquid of similar specific gravity 

 to themselves. A vast proportion, constituting the loAvest and fun- 



* " The blood [damo, lli-hr?^ is the life." — Deut. xii. 23. " o:>.a . . . iv Tovr(f 

 yap eart 7/ ^vxv-" — Josiphus, Antiq. I. 3. 8. " Empedoclcs," says riutarch, "con- 

 siders the soul to be the blood i)oured into the heart." Homer (Odyssey, xi. 36. 

 97. 147.) says, " The shades thirst after blood, for by its influence they escape from 

 Erebus, and regain speech." See also Sprengel, " IJeitriige zur Ceschichte dcr 

 Medizin," i. 3. for the belief by the ancients in the vitality of the blood. 



Germ of a Rabbit 

 (Barry). 



