Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0101clau Year: 1884 HTDROZOA SIPHONOPHOBA. 245 possess a circle of tentacles. They always, however, have a long tentacle arising from their base. This tentacle can be extended to a considerable length, and be retracted into a spiral coil. It rarely has a simple form, but, as a rule, it bears a number of unbranched lateral twigs, which are also very contrac- tile. These tentacles are invariably beset with a great number of nema- tocysts, which in many places are closely packed and have a regular arrangement.

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Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0101clau Year: 1884 HTDROZOA SIPHONOPHOBA. 245 possess a circle of tentacles. They always, however, have a long tentacle arising from their base. This tentacle can be extended to a considerable length, and be retracted into a spiral coil. It rarely has a simple form, but, as a rule, it bears a number of unbranched lateral twigs, which are also very contrac- tile. These tentacles are invariably beset with a great number of nema- tocysts, which in many places are closely packed and have a regular arrangement. These aggregations of thread-cells are especially found on the lateral branches of the tentacles, and give rise to large, brightly-coloured swellings, the batteries of nematocysts. The batteries show considerable variations a I FIG. 187.—Group of buds of a Physophor at the bottom of the pneumatophore. C, Central cavity ; S/c, nectocalyx bud with the ectodermal ingrowth.

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