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NATURAL HISTORY. 



M A G N I F I E 1) 

 "WITH A HUD. 



a simple internal structure, and may or may not be provided with a mouth and a gastric cavity. This 

 is simple and without oesophagus and divisions, and is ciliated, as a rule. Tubes may pass from it in 

 some large forms. The nervous system is neuro-muscular in the fixed forms, and there is a rudimentary 

 nervous structure in relation to the marginal canal and lithocysts of the medusae. The sexes are 



separate, and the colonies contain male and female stock, besides those destined 



for alimentation. 



The Hydroida, therefore, consist of colonies of polypes, more or less dendroid 



or cespitose in shape, which produce sexual buds, which often bear free medusje. 



The order contains several sub-orders, such as the Hydrocorallinse, the Tracho- 



medusse, the Tubularife, and the Campanularise, of which the last two are the more 



closely allied, and are very typical of the order. 



SUB-ORDER TUBULARIA. 



Dr. Allman found in the Firth of Forth, in the month of June, whelk- 

 shells covered with a mossy-looking growth, which, on a slight magnifying power 

 being applied, proved to be a number of polype-looking things, having their 

 stems united at their bases by a set of roots, and having tentacles at the other 

 end. Some of the stems were narrow where attached to the roots, and became 

 smaller near their ends, which diminished in size, and resembled small cones. At 

 'ATTACHED TO * ne ^P ^ ^ ne cone i g a sma ll mouth, and just below it is a circle of six to ten 

 DUCKWEED ; B, tentacles, some projecting outwards, and others upwards and downwards. On the 

 stem, but not reaching up as far as the tentacles, is a skin roughened with particles 

 of sand, and a more delicate one extends to the mouth. Some of these stems had 



an offshoot made like themselves. They were about two lines long. Very contractile on irritation, 



and having the power of killing prey with nematocysts, which occur in bundles on the tentacles, 



these stems receive food and digest it, and are the nourishing parts of the colony. 



A second kind of stem exists, but it is very small where it joins the common root, and then it 



becomes suddenly globular, and has neither opening 



nor tentacles when small. This kind has nothing 



to do with nutrition, but is part of the repro- 

 ductive apparatus. For in June the globular mass 



enlarges, and becomes transparent, and after a, 



while it bursts, and a small Medusa or Jelly-fish, 



egg-shaped at first, but growing more ball-shaped, 



escapes. This has two long tentacles on the edge 



of its umbrella, and the mouth within has four 



shallow lips. It is a pale reddish little thing, and 



moves after the fashion of larger ones. Leading a 



free-swimming life, and taking in food, it produces 



eggs which, after hatching, settle down, and each 



one becomes in the year following a colony of the 



stems just noticed. Such an animal belongs to the 



Hydroida, and from having the generative bud 



and tentacles of the stern uncovered by any special 



hood, it is called one of the gymnoblast* group, 



or sub-order. 



The species is Perigonimus vestitus, and the 



genus was named by Sars from the fact that some- 

 times the medusa buds are found around the nutritive stems (Greek, peri, around; gonimos, 



productive). It belongs to the family Eudendridse, of the Gymnoblastea.f 



* Greek, yymnos, nakeil ; llastos, bud. 



t Certain terms are employed to describe the Hydroids, and if the description of the species of Perigonimus be referred 

 to, the terminology becomes easy of comprehension. The entire colony, with all its parts, stems, and roots, is the Hydrosoma 

 (Greek, hydra, a monster ; soma, body). The stems which are nutritive only form the Trophosorne (Greek, trophe, nourishment; 



(After Allman.) 



