ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 789 



nerves. He shows inter alia that the ventral organ, or rather the 

 abdominal respiratory movements are controlled from two centres, 

 the metathoracic and the cephalic ganglia. The excitation of the 

 thoracic organs is less satisfactorily investigated, but here again it 

 seems most probable that there are no special luminous nerves, and 

 that the organs are exclusively influenced by muscular contractions. 

 A corroboratory experiment in which the luminosity was excited by 

 blowing in air, beautifully confirmed the above results. 



/. The effect of artificial stimuli. — The blaze of light results 

 solely from the oxygen expressed from the tracheae ; mechanical, 

 chemical, and electrical stimuli (on excised organs of course) only 

 effect the lesser light already referred to. Mechanical irritation was 

 most effective, though some chemical reagents gave an approximate 

 result. For the results of the thirty or so chemical reagents, and of 

 the immense number of electrical experiments (conducted under great 

 difficulties of deficient apparatus), it is only possible here to refer to 

 the summary given in the memoir (pp. 369-377). 



g. The nature of the luminous process. — Beyond the fact that the 

 luminous function depends on an oxidation process, hardly any certain 

 statement can be made. During luminosity a greenish-yellow pigment 

 seems to be formed, but the import of the observation is not yet 

 determined. Herr Heinemann expresses his opinion that the proto- 

 plasm of the luminous cells forms a definite substance, 'luminous in 

 contact with oxygen. The organs are probably peculiarly modified 

 skin-glands, and the formation of this specific substance is comparable 

 to the activity of glandular cells. What the substance is Herr 

 Heinemann hopes to discover by further research. He was hindered 

 from following up its resemblance to white phosphorus, by the 

 impossibility of obtaining even a fragment of phosphorus in Laguna 

 de Terminos ! 



Glands of Insects— A new type of Elastic Tissue.* — M. J. Gazag- 

 naire states that the so-called elastic cells described by M. Viallanes 

 in Eristalis as a new type of elastic tissue are merely unicellular 

 glands, which have a lubricating function. 



Nature and Origin of the Spiral Thread in Trachese.f — Weiss- 

 man has described the origin of the " intima " and of the spiral thread 

 of tracheae in insects, and has shown that the peritoneal membrane of 

 the trachea is the inpushed epiblast, while the " intima " is merely a 

 sort of cuticular product of this peritoneal epithelium. Dr. A. S. 

 Packard gives the name " endotrachea " to this cuticle, and " ecto- 

 traohea " to the epithelium which produces it. By the study of 

 transverse sections through the pupa of Datana sp., he concludes that 

 the so-called spiral thread is not really spiral, but is a series of circular 

 thickenings of the endotrachea; these thickenings or "taenidia" may 

 extend all round, or they may, as at the branchings of a trachea, only 

 partly surround the tube. 



* Comptes Eendus, cii. (1880) pp. 1501-3. 



t Amer. Natural., xx. (18SG) pp. 438-42 (3 figs.). 



