196 SUMMARY OF CURRENT RESEARCHES RELATING TO 



wards, and also takes account of the development of the musculature, 

 the glands (in Lema, &c), and the chitinous spines. 



Egg-laying of Hydrophilus piceus.*— Dr. Fischer-Siegwart describes 

 the process of cocoon-formation and egg-laying in this beetle. A speci- 

 men kept by him in captivity produced three cocoons at intervals of 

 three days, each cocoon giving rise to about fifty larvae. The period 

 of development is about five days, the larvae quitting the cocoon on the 

 sixth day. At the time of emergence the larvae; are 12-15 mm. in 

 length. 



Pygidial Glands of Carabidse and Dytiscidse.f— Fr. Dierckx gives 

 a very detailed account of these structures. In Oarabidse the pygidial 

 gland is situated on some part of the rectum ; it always consists of a 

 more or less compact group of pseudo-acini, a collecting canal, and 

 a reservoir. The extremely volatile, indeed explosive, secretion was 

 studied in Brachinus crepitans. In Dytiscidae the pygidial gland is 

 double; it consists of a long infestinc-like secretory tube with one or 

 two lateral diverticula, and of a slightly muscular ovoid reservoir com- 

 municating with the exterior by a tortuous canal of minute calibre. 

 The discharging pores are found on the posterior fold of the pygidium, 

 in front of the anal sphincter. It does not seem to be defensive, but 

 rather an oil-gland, facilitating respiration. The true defensive struc- 

 ture is the rectal pouch. But this brief report does not sufficiently 

 suggest the thoroughness of the study which Dierckx has made. 



Larva of Eristalis tenax L.$ — Herr Bruno Wahl has made a special 

 study of these " rat-tailed " larvae, directing his attention chiefly to the 

 respiratory system and the imaginal discs. In studying the tracheal 

 system, it was found that beautiful preparations could be obtained by 

 injecting glycerin into the body-cavity. The glycerin rendered all 

 the tissues quite transparent, so that the whole trache.il system showed 

 up clearly. The system is of the metapneustic type, the stigmata in 

 the tail being the only ones open. The gross anatomy of the system 

 is described in detail, the most notable point being that, in addition to 

 the segmentally arranged tracheal branches, there are others which show 

 no relation to the segments. The " anal gills " are also described in 

 detail. They are twenty in number, and are blind tubular outgrowths 

 of the hind-gut, so that they are ectodermal in origin. They can be 

 protruded and retracted by special muscles, and contain tracheae which 

 are probably to be regarded as specially developed branches of the gut- 

 tracheae of the eighth segment. Apparently they function as accessory 

 respiratory organs in cases where the surrounding mud is peculiarly 

 foul ; in the everted condition they exhibit rhythmic movements. In 

 the " tail " or breathing-tube are two tracheal stems which expand into 

 stigmatic chambers at the tip. These each open by two permanently 

 gaping orifices to the exterior. Accompanying the tracheae are two slender 

 canals which open to the exterior beside the stigmatic openings, and are 

 the ducts of certain remarkable unicellular glands placed in the breath- 

 ing-tube. The secretion is oily, and seems to have a double function : 



* Arch. Sci. Phys. et Nat , viii. (1899) pp. 494-5. 



t La Cellule, xvi. (1S99) pp. 63-176 (5 pis.). 



I Arbeit. Zool. lust. Wien, xii. (1899) pp. 45-98 (5 pis. and 2 figs.). 



