TUBULARIA. 9 



as prominences indicate originating palpi, the swelling extremities of the 

 tentacula refine into points : the animal, still a simple hydra, endowed 

 with locomotive faculties, reverses its position, and becomes permanently 

 rooted on the plane supporting it. 



Such is the issue of the process generally followed by Nature, and 

 that sometimes within twenty-four hours of expulsion of the embryo from 

 the ovarian cyst. — PI. III. figs. 20-26. 



But sometimes, also, the embryo is retained in the cyst until de- 

 velopement is discovered by partial protrusion of the tentacula from its 

 orifice.— Figs. 16, 17, 18. a. 



As most naturalists deny that the inferior animals are truly vivi- 

 parous, they may ask. Whether an ovum, an embryo, or a foetus, has been 

 thu* expelled, particularly as the use of these characters is often too indis- 

 criminate. By an ovum may be understood a certain organic formation, 

 derived from the parent, involving the elements of a germ susceptible of 

 the institution of life : — by an embryo, that evolution of the germ into 

 such definite form as may be recognised by the beholder ; — and by 2, foetus 

 that approach to maturity by the development of those essential organs 

 which shall admit protracted existence, and the means of maintaining it 

 after separation from the parent. 



But nothing can be more obscure than the precise nature of what we 

 denominate the germ : whether it be a recent organic atom, derived im- 

 mediately from the parent, by some secretory process, and lodged in an 

 invisible cyst or cell ; whether of primordial origin it has subsisted as an 

 atom, until the successive maturity or decay of preceding atoms wherein it 

 was involved has set it free, that now, from concurring circumstances and 

 conditions- its own evolution may ensue. Neither is the commencement 

 of the embyronic state to be sufHcieutly defined, farther than signifying 

 the sensible formation of parts to be modelled for their respective functions 

 in final perfection. 



Nevertheless, we may conjecture that the germ is a vascular speck, 

 originally eluding the observer's view, which becomes susceptible of the 

 institution of life on attaining some certain stage or condition of its ex- 

 istence ; that the presence of life admits the evolution of the various 



VOL. I. B 



