The Construction of the Vertical Lines

These are usually no longer than an inch in the case of glow-worms living on banks outside, but may be much longer as in caves like Waitomo and Waipu. It has been stated that in Waitomo the lines may be 24 inches in length, but this is said to be exaggereted, 16 or 17 inches being the longest. We have seen vertical lines 3 inches in length within a hole in an outside bank. The problem is how the glow-worm constructs such long lines. Those even a foot long must be comparatively weighty and perhaps could be difficult for the glow-worm to manage. However, it must be remembered that the glow-worm is surprisingly strong, and can push aside and escape from a 1-inch square coverslip with water between it and the slide.

On the banks at Arapuni, at night, it is possible to find some glow-worms in the act of producing new vertical lines. In Text-fig. 1, Fig. 1, the new line, the sixth, is seen to be held in the mouth of the glow-worm. The worm presumably first produces a mucus droplet, in the centre of which runs the silk thread: this is lowered, and the silk thread is lengthened and another droplet is produced. During the secretion of the mucus droplet, the worm makes slow, convulsive movements at its anterior end which appear to be peristaltic, and the mucus collects around the head as in Text-fig. 1, Fig. 2, M. The worm pulls its head out of the droplet, which remains on the silk thread. Something like this observation was previously made by Albert Norris. So far as can be judged from quick examination by flashing on the light at intervals so as to alarm the worm as little as possible, the production of the mucus droplet is not rapid. From the anatomy of the parts concerned, we know that the musculature of the mucus glands is scanty, and the mucus has a considerable distance to pass along the oesophageal valve and oesophagus. In the previous paper it was shown that about 60 mucus droplets had been produced by a captive glowworm in the space of three hours, but not all this time had been devoted to mucus secretion. There is no evidence that the worm cuts and adds lengths to an already constructed and fixed vertical line, and the only possible conclusion is that very long lines have been secreted at one sitting by one glow-worm, and have been lowered from above. If a vertical line is removed by fine forceps and laid on a glass slide for examination by the microscope, the droplets are seen to contain a small number of short, opaque inclusions as depicted in Text-fig. 2, Fig. 5A. The nature of these stick-like bodies is unknown; they may assist in keeping the mucus droplets in situ. So far as could be ascertained, each droplet is nearly spherical when secreted, but certainly in snares outside on banks, becomes somewhat irregular, presumably by evaporation. It will be seen in Text-fig. 2, Fig. 5A. that the droplets tend to pull down to a pyriform shape, and the silk thread in the initial droplet (the lowermost of the three) may be turned up. In some cases it is frayed at the end. Good preparations of the snare were made by holding a cover slip vertically and wiping the snare on it. When dried these smears stain well in Leishmann's blood stain, the silk being deep blue, the mucus reddish. The droplets are not so sticky as those on the snare of the British Epeira, nor is the silk so strong as in this spider. The multiple silk line (or lines) which forms the horizontal runway is very strong.