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6. Instructions on the Collection and Preservation of 

 Hydroids and Polyzoa. By G. J. Allman, M.D., 

 P.L.S., F.E.S. 



Hydroida. 



In the notes on the towing net reference is made to the 

 Hydroid Medusae as among the objects most frequently captured in 

 the net ; and it is stated that these almost always originate as 

 buds from rooted plant-like zoophytes. These hydroid zoophytes 

 grow like sea-weeds beneath the sea ; the buds, which when ma- 

 ture detach themselves and spend the remainder of their lives as 

 free-swimmers in the open sea, are the sexual portion of the hydroid 

 colony, and are destined to give origin to generative elements, 

 inale and female, by which the species is perpetuated, while the 

 rooted plant-like portion consists for the most part of a multitude 

 of little hydranths or polypites destined not for generation but for 

 nutrition. These are minute flower-like bodies, each with a mouth 

 occupying the, central point in the flower, and surrounded by con- 

 tractile tentacles which are mostly so disposed as to resemble the 

 petals and other verticils of a regular flower ; the whole of the 

 hydranths are organically united into a composite rooted colony. 

 In many cases, however, the generative buds do not detach them- 

 selves at any period of their existence, and then they form, like the 

 hydranths, a permanent plant of the common colony. The rooted or 

 nutritive portion of the colony is the trophosome ; the assemblage 

 of generative buds whether permanently fixed or destined to be- 

 come free is the gonosome. When these buds become free, as in 

 the case of the medusae above referred to, they may be named 

 planoblasts. A few words on the modes of collecting the tropho- 

 somes may here be added to what has already been said regarding 

 the planoblasts. 



While the planoblasts must be sought for by the towing net, the 

 rooted trophosomes are obtained by means of the dredge or by 

 examining the rocks left exposed by the retiring tide. There is 

 scarcely any depth at which these beautiful organisms may not be 

 encountered by the dredge, but they are most abundant in moderately 

 deep water. They here fix themselves to masses of rock or to 

 old shells, or to sea- weeds or other bodies affording a sufficient 

 surface for attachment, and in some rare cases they root themselves 

 in the sandy sea bottom. The region between tide marks will at 

 low water often afford a rich harvest to the collector. Here the 

 hydroids will be found rooted to the sides of rock pools or fixed in 

 the clefts or under the projections of the rocks, or spreading over 

 the surface of exposed sea-weeds. Large loose stones lying be- 

 tween tide marks ought to be turned over, and the under surface 

 examined for hydroid trophosomes many of which are chiefly found 

 in such situations, especially on stones which lie near the extreme 

 limit of low water. If any portion of the stones or rocks on which 

 they grow can be broken off and carried away with them so much 

 the better ; if not, they are to be detached by means of a broad 

 knife blade passed under their point of attachment. When growing 

 on shells they ought not to be separated from these. If the shells 

 be too large these may be broken and the fragments preserved with 



