MULTICELLULAR ORGANISMS. 95 
Fies. 41 to 46.—In the following figures, ec, denotes ectoderm ; en, endoderm ; t, tentacle ; hp, 
hypostome ; f, foot ; ts, testes ; ov, ovary ; ps, pseudopodium ; ec’, larger ectoderm- cells : 
ne’, larger nématocysts before ‘rupture ; ep, Kleinenberg’s fibers ; c.l, supporting lamella ; 
el, chlorophyll forming bodies ; c, cilium 
Fie. 41 .—The green hydra, at the maximum of contraction and elongation of its body. The 
creature is represented i in the act of seizing a small crust A, 2). 
Fia. 42.—Transverse section across the body of a hydra, in the "aigeRtlve cavity of which a 
small crustacean is represented. 
Fia, 43.—The leading types of thread-cells, after liberation from the body (F, 3). The cells are 
represented in the active and the resting conditions; in the former all the parts are more 
distinctly seen in consequence of the necessary eversion. 
Fic. 44.—Small portion of a transverse section across the body of a green hydra (D, 3). 
Fig. 45.—A large brown hydra bearing at the same time buds produced asexually aud sexual 
organs. 
Fie. 4 .—Larger certs HS the ectoderm isolated. Note the processes of the cells or Kleinen- 
berg’ 's fibers. 3.) 
All - oT e cuts on oaes! 9, 11, 13, 16, 18, 21 and 24, have been selected from Howes’ *' Atlas of 
iology.”” 
budding, and when cut into portions each may become a com- 
plete individual. However, under other circumstances, near 
the hases of the tentacles the body wall may protrude into little 
masses (testes), in which cells of peculiar formation (sperma- 
tozoa) arise, and are eventually set free and unite with a cell 
(ovum) formed in a similar protrusion of larger size (ovary). 
Here, then, is the first instance in which distinctly sexual re- 
production has been met in our studies of the lower forms of 
life. This is substantially the same process in Hydra as in 
mammals. But,as both male and female cells are produced by 
the same individual, the sexes are united (hermaphroditism) ; 
each is at once male and female. 
Any one watching the movements of a Polyp, and compar- 
ing it with those of a Bell-animalcule, will observe that the 
former are much less machine-like; have greater range; seem 
to be the result of a more deliberate choice; are better adapted 
to the environment, and calculated to achieve higher ends. In 
the absence of a nervous system it is not easy to explain how 
one part moves in harmony with another, except by that process 
which seems to be of such wide application in nature, adapta- 
tion from habitual simultaneous effects on a protoplasm capable 
of responding to stimuli. When one process of an Ameceba is 
touched, it is likely to withdraw all. This we take to to be due 
to influences radiating through molecular movement to other 
parts; the same principle of action may be extended to Hydra. 
The oftener any molecular movement is repeated, the more it 
tends to become organized into regularity, to become fixed in 
its mode of action ; and if we are not mistaken this is a funda- 
mental law throughout the entire world of living things, if not 
of all things animate and inanimate alike. To this law we 
shall return. 
But Hydra is a creature of but very limited specializations; 
there are neither organs ef circulation, respiration, nor excretion, 
