52 ALLMAN. HYDROIDS AND POLYZOA. 



the hydroids attached to them. When growing over the surface 

 of sea- weeds the portion of the plant to which the hydroids have 

 attached themselves ought also to be retained. When thus secured 

 no time should be lost in placing the specimens in spirit, for when 

 exposed to the air they very soon dry up and lose some of their 

 most important characters. 



POLYZOA. 



The Polyzoa often resemble the hydroid trophosomes so closely 

 that the inexperienced collector can scarcely be expected to dis- 

 tinguish them, and indeed on this point he need not trouble himself, 

 for the determination of their distinguishing characters may well 

 be left to future careful examination. Like the hydroids they form 

 for the most part plant-like colonies, sometimes giving rise to 

 branching colonies like tufts of sea-weed, and sometimes spreading 

 like lichens over the surface of stones, shells, and algae. The cir- 

 cumstances under which they occur are almost entirely the same as 

 in the case of the hydroid trophosomes, and they are to be collected 

 and preserved in the same way. 



7. Instructions on the Constkuction and Method of 

 Using the Towing Net, and Notes on the Animals 

 which may be obtained by its employment. By 

 G. J. Allman, M.D., RL.S., F.RS. 



Construction of the Towing Net. 



The towing net is a small bag made of some material open 

 enough in its texture to allow of the water easily passing through 

 it, and yet sufficiently close to retain within it such minute bodies 

 as it may encounter in its passage through the sea. Its mouth is 

 kept open by a strong ring, and it is towed behind the vessel by 

 means of a line fastened to the ring. 



The bag may be made of fine straining-linen or of new bunt- 

 ing ; and in the size which will be found most generally useful it 

 may have a depth of about 18 inches, and a width across its 

 mouth of about a foot. The ring which surrounds the mouth 

 may be a wooden hoop ; or it may be made of brass rod strong 

 enough to resist the tendency to become bent when the net is 

 being drawn through the water. 



Three pieces of strong line about two feet in length are to be 

 fastened at equal intervals to the ring, and tied together securely 

 at their opposite ends. To the point of their union the towing 

 line is to be attached. With a net of the size here suggested, a reel 

 of strong " hake-line " will make the best towing line for all the 

 ordinary velocities at which towing may be most advantageously 

 practised. 



Mode of Using the Net. 



When thus rigged the net may be used from a row boat, or 

 from a sailing vessel or steamer under moderate way. It may be 

 thrown out from the stern ; and in surface-towing sufficient way 

 must be given to keep the mouth of the bag close to the surface 

 of the water. Many of the small objects which may be floating 



