PLANKTONIC STUDIES. 569 



Although these negative coiichisious fi-om the so-called " exact ex- 

 periments" of Agassiz are contradicted by the foregoing results of the 

 Challenger investigator, yet against the latter, with some show of right, 

 Agassiz might have raised the objection that the ''tow net" used could 

 establish no safe conclusion.* This objection could only be finally 

 removed by the construction of a new tow net, which could be let down 

 closed to a certain depth, and then opened and closed again. The 

 merit of inventing such a closible net, and of the immediate successful 

 use of it, belongs to two distinguished Italian naval officers : G. Pal- 

 un)bo, commander of the Italian war corvette Vettor Pisaiii, first con- 

 structed such a closible pelagic net or "bathy graphical zone net;" and 

 Naval Lieutenant Gsetano Chierchia, who during the three years' voyage 

 of the Vettor Fisaxi around the world made a very vahiable collection 

 of pelagic animals, used the new closible net with fine results, even at 

 a depth of upwards of 4,000 meters (8, p. 83). 



Chierchia's first trial with this "deep-sea closible net" was June 5, 

 1884, in the East Pacific Ocean, directly under the equator, 15° west of 

 the Galapagos Islands. Fourteen days later, June 19, midway between 

 the Galapagos and the Sandwich Islands, this closible net was sunk to 

 4,000 meters. In this and in many other trials these Italian naval 

 officers captured an astonishing wealth of new and interesting zonary 

 animals, whose description has for a long time busied zoologists. The 

 collections brought back to Naples by the Vettor Pisani are, next to 

 those of the ChaUenger, the most imi)ortant materials from the region 

 under coi i sideration. 



A few faults which pertained to Palumbo's net were soon done away 

 with by improvements, for which we are indebted to the engineer Peter- 

 sen and to Prof. Carl Chun, of Breslau. The latter, in 1886, made 

 trials in the Gulf of Naples with the improved closible net which 

 showed "a still more astonishing richness of pelagic animals in greater 



* The " tow nets " used by the Challenger were the ordiuary Miiller's net (or the 

 " fine pelagic net" of Joh. Miiller), a round bag of Miilhn- gauze or silk mull, the 

 mouth being kejit open by a circular metallic ring. This ring is iu ordinary pelagic 

 fishing fastened to a handle 2 or 3 meters long (like the ordinary butterfly net). 

 While the boat moves along, the opening of this net is held at the surface in such a 

 way that the swimming animals are taken into the bag. They remain hanging 

 in the bottom of this, while the water passes through the narrow meshes of the net. 

 After a time the net is carefully inverted and the tow stuff (Attftrieb) is emptied 

 into a glass vessel filled with sea water. If one wishes to fish below the surface, 

 the ring of the net is fastened by means of three strings, equally distant from one 

 another, which at a point (about 1 meter distant from the opening of the net) are 

 joined to a longer line which is sunk by weights to a definite distance, correspond- 

 ing to the desired depth. When Murray fastened such a tow net to the deep-sea 

 sounding line or to the long line of the deep-sea dredge, he first obtained the inhabi- 

 tants of the " intermediate ocean zones," but he could not thereby avoid the objec- 

 tion that, since this tow net always remained open, the contents might come from 

 very different depths or even only from the surface. For iu <lrawing up the open 

 tow net animals from the most different zones of depth might occasionally be taken iu. 



