386 SUMMAEY OF CURRENT RESEARCHES RELATING TO 



assemblage of miuute Hymenoptera. It lays its egg on the egg-mass of 

 a beetle, Donacia simplex, a single parasite emerging from one ^^g of 

 the host. The ovum has a large germ-cell determinant at its posterior 

 pole, and in segmentation the determinant is divided among the large 

 cells in that area. These are the germ-cells. In the single case fomid 

 there were two polar bodies. The blastula is fairly normal, except for 

 a curious arrangement of the chromatin in the somatic nuclei. Many 

 nucleoli are cast out into the centre of the egg, where they collect till 

 twenty-five to fifty are present ; the mass is then extruded on the 

 periphery of the egg. As the blastoderm grows it broadens without 

 lengthening up to the stage where the germ-layers begin to form. 

 About thirty-five nuclei sink inwards from the dorsal surface of the 

 embryo to form endoderm. From the blastoderm stage to that of the 

 gastrula no nuclear division appears to take place. Shortly after the 

 formation of the endoderm amitosis may be found, and from this 

 onwards the number of nuclei increases. The mesoderm seems to be 

 formed from peripheral nuclei which sink in sporadically ; no somites 

 can be made out, nor does any segmental method of formation of the 

 mesoderm occur. The nervous system, stomodeeum and probably 

 proctodseum are normally formed. The germ-cells lie in a pocket 

 formed by several somatic cells which embrace them. Ordinary mouth- 

 parts, tracheae, heart, and oesophageal valve are wanting ; the head has 

 two horn-like mandibular processes, which may assist in scooping 

 forwards the food. The larvae does not feed on the food little by little, 

 defecating as it eats ; instead, it begins by swallowing all the yolk at 

 once, so that its body becomes enormously distended and stretched. 

 Metameric external segmentation is absent, the body and head being 

 continuous and sac-like. 



Black Markings on Wings of Large Cabbage Butterfly.* — Herbert 

 Onslow finds that the black markings on the wings of Pieris drassicse 

 are caused by the oxidation of a colourless chromogen by a tyrosinase. 

 This ferment is supplied from the body-lymph of the pupa, possibly 

 by means of the wing-nervures, to the chromogen which has previously 

 been deposited in the areas destined to become black. The form of the 

 markings is determined by the localization of the chromogen to these 

 areas. The oxidation takes place just l^efore the emergence of the fully- 

 developed insect, and as soon as the atmospheric oxygen has access to 

 the surface of the wing. 



Aquatic Lepidoptera.j — Welch finds that eggs of Nympliula 

 inamlalis are invariably deposited about the egg-holes of a Chrysomelid 

 beetle {Donacia) in the floating leaves of the yellow water-lily. Tracheal 

 gills appear in the second instar. There are forty filaments in the 

 second instar, over four hundred in the full-grown larva. Excised pieces 

 of leaves form a case, serving for protection and support in the water. 



* Biochemical Journ., x. (1916) pp. 26-30. 



t Arm. Entomol. Soc. Amer., is. (1916) pp. 159-90. See also Trans. Amer. 

 Micr. See, XXXV. (1916) p. 261. 



