- single series, - nile polyp. budding out one, which. dianetidileten 
summit one, this another and so on. In figure 10 there are two 
series; the axis lengthens between the two terminal and then 
buds again other two at the extremity, and so the branch lengthens. 
In figure 11 there is a series of clusters, the. (hana pone? be- 
ing in. part intermittent. 
In some Tubularide, certain caducous waco oaeiie into 
‘dalicgta flat memberless animals resembling a Planaria, and which 
_consequently were called planules by Sir J. G. Dalyell.* These, 
‘according to Van Beneden, are the developments of the buds al- 
ead to on.a preceding page, ($ 17,) which contain ova. 
- 23. Connected with the process of growth and reproduction, 
‘there is a corresponding process of dying often going on in the 
older. parts of a zoophyte: the polyps disappear, and the lower 
branches often drop off, leaving the trunk in this part bare. 
‘These zoophytes are thus dying and budding in different parts at 
' the same time. In the large species, the main stem or midrib of 
the zoophyte becomes lifeless, or a mere support for the numer- 
ous lateral plumes or branchlets. 
24. Besides this mode of limiting the existence of these polyps, 
- Some Hydroidea are said to be absorbed in their cells, and after a 
while to reappear again ; and this has been observed to take place 
_ at nearly regular intervals. All the polyp cells of a living group 
have been found, after a certain period, empty, or with patie the re- 
mains of the wasted polyps, the fluid of the trunk showing the only 
prilenes of vitality by its continued vibration. And in the course 
of a few days other polyps have appeared in the vacated cells, 
_.. with the same perfection of form and. the same activity and life 
_ astheir predecessors. The polyp heads, as Sir J. G. Dalyell states 
¥ respecting a 'Tubularia, sometimes seem to drop off like a decidu- 
ous flower, and again, after ten days or more, are reproduced. Har- 
vey observes, that after he had kept his specimens two days, 
they began to look unhealthy ; and on the third “the heads were 
all thrown off, and lay on the bottom of the vessel.” After an- 
other three days, changing the water in the mean time, the 
polyps were entirely renewed, with no essential difference, expept 
absence of color. The cold of winter 
; sR of its Perr pore which remains thus apparently eid til 
* Rep. Brit. Assoc. for 1834, p. 602. 
