580 SUMMARY OF CURRENT RESEARCHES RELATING TO 



trace the changes of some one characteristic, e. g. length of wing, during 

 several successive generations. Three lines of descent will be contrasted, 

 viz. shortest winged, longest winged, and medium winged, in each 

 generation. 



For measuring the length of wing of living moths, he proposes a pair 

 of scissor-like compasses, with arms on one side of the joint, being five 

 times the length of those the other side, and the long arms furnished with 

 an index marked in 1/2 millimetres. He has also tried the glasses from 

 one of the tubes of an opera-glass, with a lengthened interval between them, 

 so as to form a Microscope of very long focus, say 18 in. This was fixed 

 to a light rod that carried a millimetre scale, set across its free end, at a 

 trifle less than 18 in. from the object-glass. On approaching the scale to 

 within half an inch of any small object, that object and the scale are both 

 in fair focus at once, and they are sufficiently far from the eye to render 

 any error (arising from slight change in position of the eye) of little or no 

 importance. 



For accurate measurements of dead moths, Mr. Galton has a much 

 better instrument under construction, in which there is a small Microscope 

 with cross wires, in the short limb of a pentagraph, the long limb being 

 used both for setting the Microscope and for reading ojff the measurements. 



The author then details his method of centering the measurements, by 

 means of a curve through the ends of ordinates, such as he has used in 

 other measurements. 



Histology of Enteric Canal of Insects.* — M. V. Faussek has observed 

 in Eremohia muricata the same kind of glandular structures between the cells 

 of the cylindrical epithelium of the midgut, to which Frenzel has applied 

 the name of glandular crypts. They have the form of narrow-necked flasks, 

 and are filled by a mass of closely applied nuclei, which do not differ essen- 

 tially from the nuclei of epithelial cells. The hind-gut consists of two 

 sections, connected with one another by a delicate coiled tube. This has 

 a strong muscular layer, and is lined by an epithelium, which consists of 

 very small cells, is raised up into folds, and provided with a thick intima. 

 On the contraction of the muscular elements, these folds must close the 

 lumen of the tube. In the portion of the tract which lies above the con- 

 necting tube, the epithelium consists of long broad cells, with very large 

 nuclei, each of which is surrounded by a transparent area. The other part 

 of the tract is occupied by six longitudinal ridges of the epithelial layer — 

 the so-called rectal glands. In the epithelium of these there are two kinds 

 of cells, some being higher and cylindrical, others less distinctly marked 

 and mucous. The nuclei of the latter are of small size, and each occxxpies 

 the centre of a clear vesicular space. The space between the epithelial 

 layer and the musculature is filled by a loose fibrous connective tissue, the 

 limits of the separate cells of which are not preserved. The tracheae 

 branch in this tissue, and fine ramules make their way between the epithelial 

 cells, and end in small blind enlargements. 



Some interesting observations were made on the structure of the hind- 

 gut in larvas of ^schna and Lihellula. The muscular layer is feebly, but 

 the epithelial well developed. The latter consists of two kinds of cells in 

 different regions. Some are large and cylindrical, with large granules, and 

 these form folds, into which enter pretty thick tracheal branches. This 

 kind passes gradually into the second, in which the cells and their nuclei 

 are small ; and the protoplasm does not stain with carmine. The layer formed 

 by these is arranged in numerous complicated folds, and appears in cross 



* Zool, Anzeig., x. (1887) pp. 322-o. 



