. Journal of experimental zoology. amilla and Sabellawere due in part to their comparative indifference to the varioustests applied. EXPERIMENTS ON HYDROIDES DIANTHUS The general character of these annelids is so well known that noparticular account is necessary. The photographs of several typi- 298 Chas. W. Hargitt cal conditions will show quite enough to make clear the habitat andmodes of growth. Colonies growing upon shells are seldom large,while those growing upon rocks are frequently quite large, oftenincluding from thirty to fifty, or even more, distinct specimens,eachinhabiting its own
. Journal of experimental zoology. amilla and Sabellawere due in part to their comparative indifference to the varioustests applied. EXPERIMENTS ON HYDROIDES DIANTHUS The general character of these annelids is so well known that noparticular account is necessary. The photographs of several typi- 298 Chas. W. Hargitt cal conditions will show quite enough to make clear the habitat andmodes of growth. Colonies growing upon shells are seldom large,while those growing upon rocks are frequently quite large, oftenincluding from thirty to fifty, or even more, distinct specimens,eachinhabiting its own tube, but forming inextricable masses vari-ously intertwined, and among which are usually various otherannelids, corals, hydroids, etc., the whole comprising a most in-teresting ecological community, as well as a most beautiful displayof richly varied form and color, rarely surpassed among the almostinfinite variety of marine life. It may be noted in passing thatmost of this richness and variety of coloration is to be iound in the. Fig. 3. Colony of Protula intestinum, from Bay of Naples. The serpentine aspects ofthe tubes referred to in the paper are easily recognized. The coiled tubes to be seen upon thecentral tube of the colony is particularly interesting as clearly indicating the indifference of thecreature to the influence of gravity. (Somewhat less than the natural size.) annelids themselves, a fact which has been long known andcommented upon, but little understood. This feature will befurther considered in connection with the several accounts inwhich it may be involved. Behavior of Tiihicolous Annelids 299 Though I had often observed the general sensitiveness of thesecreatures to sudden intervention of shadows of various sorts, myattention was particularly attracted to the matter in the presentinstance by the observation that shadows of even the slightestdegree, such as those produced by a strip of white paper, or evena glass rod, seemed quite as effective a stimulus as
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