. The Annals and magazine of natural history; zoology, botany, and geology. Natural history; Zoology; Botany; Geology. 248 M. C. Mereschkowsky on the Hydroida. support of the explanation above given of the forms with capitate tentacles. I refer to the blastostyles of the genus Hydractinia. It is well known that the gonophores, or sexual individuals, appear upon the surface of the body of the tropho- somes, or nutritive individuals, which are furnished with several filiform tentacles. When these gonophores appear, the individual upon which they are seated, and which is then called a " blas
. The Annals and magazine of natural history; zoology, botany, and geology. Natural history; Zoology; Botany; Geology. 248 M. C. Mereschkowsky on the Hydroida. support of the explanation above given of the forms with capitate tentacles. I refer to the blastostyles of the genus Hydractinia. It is well known that the gonophores, or sexual individuals, appear upon the surface of the body of the tropho- somes, or nutritive individuals, which are furnished with several filiform tentacles. When these gonophores appear, the individual upon which they are seated, and which is then called a " blastostyle," becomes much thinner and smaller (the material of the animal being absorbed by the sexual bodies), the mouth closes, and the tentacles (which, from this moment lose their importance as organs subserving the purpose of nutrition, since the mouthless individual cannot feed) become shorter and shorter and more and more insignificant. Soon we can only perceive a few knobs or tubercles furnished with a great quantity of thread-cells, greatly resembling the dila- tations with which the capitate tentacles are furnished. At the same time these tentacles or tubercles only retain the function of defence from enemies. But I have said that there are exceptions to the rule that articulation is associated with capitate tenta- cles, and that these exceptions are not con- Fig. 7. tradictory to the explanation that I have given ; on the contrary, it is possible to explain these exceptions only by admitting all that I have said above. There are some forms, evidently belonging to the articulate type, which do not possess capitate tentacles, but, on the contrary, have those organs slender, filiform, and very long. For example, Clava'^, Cordylophoraj &c. (especially Cordylojphora) have tentacles longer than in any other species. This is to be explained as follows:—In becoming developed into the articulate type the Hy- droid became more and more elongated, whilst the tentacles r
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