REPRODUCTION OF CORDYLOPHORA. 539 



female (or Pistilline) flower, whilst floating on the surface of the 

 water, after it has broken itself off from the stem. The Ova thus 

 fertilized, being deposited by the free-swimming Medusa-buds, 

 evolve themselves into single Polypes ; and from every one of 

 these is gradually produced by continuous gemmation a Composite 

 fabric, which in its turn developes Medusa-buds, whose offspring 

 resume the Polype-form.* In Cordylophora, instead of detached 

 Medusa-buds, peculiar Capsules sprout-forth from the stem, some 

 of which contain Sperm-cells and others Ova ; and the spermatozoa 

 set-free from the former enter the ovigerous capsules and fertilize 

 their ova, after the fashion of Vaucheria (§ 246). The fertilized 

 Ova undergo 'segmentation' according to the ordinary type (§476), 

 the whole yolk-mass subdividing successively into 2, 4, 8, 16, 32 or 

 more parts, until a ' Mulberry mass ' is formed ; this then begins 

 to elongate itself, the surface becoming smooth, and showing a 

 transparent margin ; and this surface becomes covered with Cilia, 

 by whose agency these little bodies, now called 'Gremmules,' first 

 move-about within the capsule, and then swim forth freely when 

 liberated by the opening of its mouth. At this period the Embryo 

 can be made out to consist of an outer and an inner layer of cells, 

 with a hollow interior ; after some little time the cilia disappear, 

 and one extremity becomes expanded into a kind of disk by which 

 it attaches itself to some fixed object ; a mouth is formed, and 

 tentacles sprout forth around it ; and the body increases in length 

 and thickness, so as gradually to acquire the likeness of one of 

 the parent Polypes, after which the Plant-like fabric characteristic 

 of the genus is gradually evolved by the successive development 

 of Polype-buds from the first-formed polype and its subsequent 

 offsets. 



415. In the Family Tubularidce, the long Polype-stems are 

 invested by tubular horny sheaths ; but these stop-short below the 

 polype-heads, which are consequently unprotected ; and the repro- 

 ductive Gemma? bud-forth, as in the preceding case, from the base 

 of the tentacles. The most common form of this Family is the 

 Tubularia indivisa, which receives its specific name from the 

 infrequency with which branches are given-off from the stems, 

 these for the most part standing erect and parallel, like the stalks 

 of corn, upon the base to which they are attached. This beautiful 

 Zoophyte, which sometimes grows between the tide-marks, but is 

 more abundantly obtained by dredging in deep water, often attains 

 a size which renders it scarcely a microscopic object ; its stems 



* It is to this phenomenon that the term ' Alternation of Generations ' 

 has been applied. It is, however, an inappropriate designation ; since 

 the Zoophyte and the Medusoid are really the Vegetative and Reproduc- 

 tive portions of one and the same Organism ; the only peculiarity of the 

 case being that the Medusoid is here detached and leads an independent 

 life. In many other Hydrozoa the Medusoid remains connected with the 

 parent-fabric, to which its relation as the Generative Flower-bud then 

 becomes obvious. 



