. Zoology : for students and general readers . Zoology. DEVELOPMENT OF HYDR0ID8. 59. Fig. 39. — Polypite of Coryne mirabUis, vnth& bud below a, and medusa-bud (gouophore) at a. Much en- larged.—After Agassiz. living Millepora, unless handled with great care, severely stings the hand of the collector. We now come to Hydroids which throw off a free naked- eyed medusa from the hydrarium (Fig. 39). From the centre of these free bell-shaped, minute jelly-fishes depends a hollow, open sac called the manu- brium, the cavity of which (stomach) opens into usually four canals, which radiate from the
. Zoology : for students and general readers . Zoology. DEVELOPMENT OF HYDR0ID8. 59. Fig. 39. — Polypite of Coryne mirabUis, vnth& bud below a, and medusa-bud (gouophore) at a. Much en- larged.—After Agassiz. living Millepora, unless handled with great care, severely stings the hand of the collector. We now come to Hydroids which throw off a free naked- eyed medusa from the hydrarium (Fig. 39). From the centre of these free bell-shaped, minute jelly-fishes depends a hollow, open sac called the manu- brium, the cavity of which (stomach) opens into usually four canals, which radiate from the hollow or stomach in the centre of the disk and communis cate with a canal following the margin of the disk. This is the water-vascular sys- tem, communicating directly with the gas- tro-vascular cavity, or stomach. Four tenta- cles hang from the disk, and simple eye- spots and otolithic sacs (simple ears) are usu- ally present and situated at regular inter- vals around the edge of the disk. Such is the typical form of all the free-swimming Hydroids. They are said, in a few cases, to possess a well-developed continuous ner- vous system, consisting of a nervous ring around the disk (Romanes). They are bi- sexual, the ovaries or spermaries being de- veloped on the radiating canals, the embryo escaping into the surrounding water by rup- turing the walls of the ovary. The young is at first oval, ciliated all over the surface of the body, and is called a planula. The planula, as in Melicertuvi, a Kg. 40.—Free Medu- genus allied to Campanularia, and a type *"^° '^*"*' of most marine Hydroids, at first spherical, becomes pear- shaped, and after swimming about for a time attaches itself to some object. It then elongates, a horny sheath {;peri-. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Packar
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectzoology, bookyear1879
