66 SUMMARY OF CURRENT RESEARCHES RELATING TO 



gut is half-invaginated into the mid-gut. The mid-gut is best developed, 

 secretory in front, and absorptive behind. There is a pyloric valve and 

 a proliferation-ring at the passage from mid-gut to hind-gut. The 

 hind-gut consists of pylorus, small intestine, and rectum. The pylorus 

 has six internal folds and strong circular muscle ; the small intestine 

 has also longitudinal ridges, but less muscle ; it is invaginated into the 

 rectum. The latter shows four strong longitudinal ridges and an anal 

 sphincter. Four Malpighian vessels open into the hind-gut at its 

 junction with the mid-gut. 



Mid-gut Epithelium of Larvae during Ecdysis.* — Max Braun has 

 studied this first of all in the caterpillar of Deilephila euphorbise. In 

 the resting larva, about to form a new cuticle, there is active karyo- 

 kinesis in the "mother-epithelium-cells" accompanied by some cell- 

 division. A regenerative syncytium is passed through as a stage, in 

 the posterior part of the gut. The details of the intricate process of 

 change are described at length. Other types used for studying the same 

 process, w^ere Hyponorneuta euonymella (Lepidoptera), Arge (Hymenop- 

 tera), CalUphora (Diptera), Melasoma, Dermestes (Coleoptera). Except in 

 Dermestes, the processes of cell-multiplication and growth in the mid-gut 

 have only to a slight extent a regenerative significance. For the most 

 part they effect the rapid increase in length and thickness after the 

 ecdysis is over. No general scheme of the changes in the mid-gut can 

 be worked out that would be applicable to all types. 



Minute Structure of Diptera. f — The late W. Wesche made a num- 

 ber of observations on the minute structure of Diptera which are now 

 published. They relate to such points as the following : — ankylosis of 

 the middle joints of the antennae in Scatopse, fused distal joints in the 

 antennae of Dilophus, the structure of the tibial bristles, peculiar struc- 

 tures in the palps of Rhyphidae and Simulidse, the pharyngeal pump in 

 various famillies, a species of Ceratopogon with mandibles, the recep- 

 tacula of Lonchoptera flaviamda^ the possible affinity of the peculiar 

 genitalia of Rhyphidae with those of Tabanidae and Leptidse, and the 

 fully developed mentum in Rhyphid^, another important link con- 

 necting the Nemocera with the Brachycera. 



«• Crustacea. 



Chromatophores of Crustacea. ^ — E. Degner has studied the chro- 

 matophores of Mysids and Decapods (Leiander treillanus and Crangoii 

 vulgar is). The changes of colour depend on intracellular pigment- 

 migration. The pigments are purely fluid, or purely granular, or con- 

 sist of solid granules in a coloured fluid. The chromatophores consist 

 of the body of the cell and the processes (chromorhizti3) which are 

 definite in number for each cell. According to external conditions, 

 the pigment is contracted or spread out in the chromorhizae. There 



* Zeitschr. wiss. Zool., ciii. (1912) pp. 115-69 (2 pis.). 



t Biol. Bulletin, xxiii. (1912) pp. 250-70 (1 pi.). 



X Zeitschr. wiss. Zool., cii. (1912) pp. 1-78 (3 pis. and 8 figs.). 



