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Previous Work
In 1915, Wheeler and Williams, of the Bussey Institute, Harvard, established the fact that the light organ of the New Zealand glow-worm consists of the enlarged ends of the malpighian tubes. Up to 1958—that is, for nearly a half century, no further information on the internal anatomy of any stage in the life cycle was available. In that year, owing to his interest in the matter, Mr. Eric C. Colbeck, of the Tourist Hotel Corporation of N.Z., published for Waitomo the present author's popularly written short pamphlet, based on work done for a year in Dublin by the present writer, and the post-graduate student Gouri Ganguly. This pamphlet described the light organ and general anatomy, but contains at least one small inaccuracy, the chordotonal sense organs should be closer within the anal papillae.
Believing at the time the various accounts claiming that the glow-worm can douse its light suddenly, Gatenby and Ganguly (1958) brought forward an explanation based on anatomical structure, as to how this might be effected. There is now serious doubt, amounting to disbelief in the writer's view, about the ability of the glow-worm to douse its light quickly when alarmed. When startled, it retreats— usually backwards—rapidly into its hiding place, and thus covers its light. It can, however, fade out its light slowly, which is something different Neither Ganguly nor the present writer had live specimens to work on, and the material forwarded
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to Dublin by Dr. Simon Cotton, of Putaruru, suffered from the fact that fixatives sent to him did not easily penetrate the cuticle of the larvae, and when instead they were teased, the parts tended to get out of position or break in transit.
Ganguly had worked for a year in Dublin, and after the present writer went abroad, she continued her study under Dr. Hinton, of the Entomology Department of Bristol University. Ganguly has given a detailed description of the histology of the larva mainly based on Bouin or Gilson fixed material. At Dublin she found the peculiar scolophores or chordotonal organs in the anal papillae of the larva, and proposed that the hydroscopic mucous droplets on the snare of this larva might be produced by the diverticula of the mesenteron. Ganguly's finding may be summarized as follows:
There is no crop. The oesophageal valve is in the first abdominal segment. The mid-gut has a peri-trophic membrane, and is histologically differentiated into three regions—the anterior secretory, the middle absorbtive region and the posterior secretory region. There are two gastric diverticula or caeca arising from the base of the oesophageal valve, and these produce the mucus. The hind gut extends from the 6th abdominal segment to the vent on the 8th segment. There is a pair of silk glands which run back to the 6th abdominal segment, then fold back to the 4th abdominal segment. Scolophore or chordotonal organs occur in the anal papillae. There are four such organs, two dorsal, two simpler and lateral. A minute thickened disc exists where the organ terminates at the cuticle. There are no cap or envelope cells in the scolophore organs. Sensory nerves pass to the last abdominal ganglion.
The malpighian tube consists of four parts, the fourth being the light organ. There are two types of fatty tissue; one pigmented, one non-pigmented. No intracellular penetrating tracheoles exist. The larva is apneustic.
It is not proposed to review the somewhat scanty previous anatomical work on related Mycetophilidae. Two forms, Ceroplatus testaceous and Platyura fultoni make webs with sticky droplets, both species being luminous. Their luminescent organs are not malpighian. Platyura is said to secrete mucus containing N/30 oxalic acid (Mansbridge). In this larva the ends of the malpighian tubules are bound to the intestinal region as in Bolitophila. In no other dipterous larva are scolophore organs yet known from the region of the anal papillae or “gills”.
In the Waitomo pamphlet, the present writer supplied a diagram of the side of the head of the larva. There are two small eyes on each side, one simple (below), the other probably partly compound (above). The antenna is quite reduced, but the circular base remains. The mouth parts have been described by F. W. Edwards (see Hudson, 1950).
As natural historians, G. V. Hudson, to whom we owe so much, and his disciple Albert Norris, were actively interested in B. luminosa. They bred adult specimens. Hudson sent many larvae, a pupal exuvia, and adults to F. W. Edwards, of the British Museum, for investigation by a skilled microscopist, whose anatomical researches, Hudson hoped, would shortly be published (Hudson, 1946). Enquiry at the British Museum by the present writer elicited the response that his successor was unable to find anything about this in the notes, etc., left by Edwards. On the interesting question of the method by which the pupa is slung from the roof, Edwards (1933) states that it hangs “by a few strong threads which, though merely a part of the larval web, may on drying appear part of the pupa itself (as was thought by Hudson)”. Hudson also sent larvae to Osten-Sacken, but so far as is known, nothing was published on their anatomy. Hudson did not at first appear to know of the work of Wheeler and Williams (1915), who examined the gut contents of the larva and recognized it as chopped up insects. But in 1892, A. Norris had proved that the glow-worm lived on other insects. Indeed, it was Meyrick,
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in 1886, who first suggested this. So far as the writer knows, Wheeler and Williams were unaware that this question had been answered by Norris.
The larvae used in Wheeler and Williams' investigation had been fixed in methylated spirit, and the correct explanation which they gave of the anatomical nature of the light organs, was not therefore made under easy conditions. Unfortunately their paper was published in a journal not well known.
Richard B. Goldschmidt (1948) discussed the adaptations of the New Zealand glow-worm for its modus vivendi. He considered that it was impossible to explain major adaptations, such as are found in Bolitophila, as having originated by slow accumulation of minute mutants through selection along Darwinian lines. Goldschmidt favoured the view that such adaptations could have selective advantage only when they were complete or almost complete. Goldschmidt misspells Arachnocampa throughout his article and attributes this generic name to Skuse. He does not add anything to our knowledge of the anatomy or habits of the glow-worm, but mentions the interesting fact that O. F. Cook found in the caves of Guatemala a larva which makes webs with hanging slimy threads.