HARDWICKE'S SCIENCE-GOSSIP. 



121 



ON MARINE COLLECTING WITH THE SURFACE-NET. 



By Dr. G. W. M. GILES. 



[ Concluded/} om p. 1 1 1 .] 



T is curious to observe 

 how the turning on 

 of the air will revive 

 an apparently dead 

 organism. I once 

 produced consider- 

 able amusement 

 amongst my topo- 

 graphical colleagues 

 in the Survey by 

 this. A small branch 

 of a hydroid zoo- 

 phyte was under 

 observation, and 

 running over it, 

 busily browsing on 

 the expanded ten- 

 tacles, was a small 

 isopod crustacean. 

 As long as the bub- 

 bles continued to 

 pass, the tentacles remained expanded, gently moving 

 in the current produced, while the isopod made 

 greedy use of his time. But within a minute of its 

 being turned off the zoophyte heads shrank up, the 

 little cannibal dropped to the bottom of the cell, 

 and both seemed to all appearance dead. On now 

 again supplying the vivifying stream the zoophyte 

 would be seen to gradually expand, and the crus- 

 tacean to pick himself up and resume his feast as 

 calmly as if nothing whatever had happened to in- 

 terrupt it. This was repeated several times, until a 

 too-protracted deprivation of oxygen killed the pair 

 in good earnest. 



If serious work be intended, as many species as 

 possible should be accurately drawn, and for this 

 purpose a camera lucida is an indispensable acces- 

 sory : one of those forms which admit of the micro- 

 scope being kept vertical being alone suitable for 

 the purpose. 



Most Crustacea are provided with such a multi- 

 plicity of variously formed appendages that it is 

 No. 258.— June 1886. 



generally practically impossible to obtain a correct 

 drawing of the whole while the animal remains 

 entire. In order to overcome this difficulty it is a 

 good plan, after drawing the body, the attachments 

 of the appendages, and such of them as are clearly 

 visible, to separate the limbs one by one from the 

 body, by dissection under the simple microscope, 

 and to arrange them in order on a glass slip. They 

 can be then readily drawn to the same scale, and the 

 separate drawings fitted on to that of the body in 

 such positions as not to hide each other. 



After the locomotive appendages have been sepa- 

 rated, the gnathopoda may be dealt with in the 

 same way, and drawn separately under a higher 

 magnification, and the remainder of the body torn 

 open and flattened out under a cover ; a proceeding 

 which will often enable one to ascertain certainly the 

 sex of the individual. 



During the process of examination and delineation 

 it will be often found desirable to substitute direct 

 for transmitted illumination, and to effect this change 

 expeditiously I find no appliance so useful as the 

 old-fashioned but much-neglected Luberkhun. To 

 stop out the central rays of light I employ small discs 

 of vulcanite, sawn out of a thin piece of sheeting. 

 By simply wetting them, these can be made to 

 adhere to any part of the under surface of the slide, 

 and can be shifted about if necessary with the tip of 

 the finger, without removing the slide from the 

 stage. By alternately employing direct and trans- 

 mitted light, many details of structure can be learnt 

 which could not possibly be made out by either 

 alone. It enables one also to fill in the natural 

 colours in the finished drawing, which are quite lost 

 by transmitted light. 



And now, as to the readiest methods of preserving 

 such organisms as permanently mounted microscopic 

 objects. I fear I shall be considered unorthodox, 

 but can only record my own impression, that Canada 

 balsam and other resinous media are quite unsuited 

 for the purpose. Soft, gelatinous creatures, such as 

 Sagittoe, Salpae, etc., are so shrunken by the action of 



G 



