54 NATURAL SCIENCE. 



feeding caterpillars of Selenia tetvalunaria, some on trees in the open 

 air and others on cut food indoors. Those treated in the former way 

 completed their development in the summer as usual ; but the house- 

 fed larvae, though they pupated in good time, did not become moths 

 until the following spring. Thus, a normally double-brooded species 

 was made single-brooded by being fed indoors, whereas the high 

 temperature of a house should have had just the opposite effect to 

 this. Mr. Merrifield finds in the condition of the food the expla- 

 nation of this anomaly. He believes that feeding on cut branches 

 wanting moisture, and with little circulation of sap, must have a 

 retarding effect on the development of the insects. 



An interesting account of the way in which the caterpillar of 

 Acvonycta alni makes its cocoon is given by Mr. M. Fitzgibbon 

 ("Entomologist," vol. xxv., p. 40). The habit of this larva is to 

 select a rotten stick, which it proceeds to hollow out, in order to form 

 a shelter wherein it may winter in its pupal stage. The noteworthy 

 point of the description is the use of the caterpillar's strong bristles 

 in sweeping away the sawdust formed by excavation. These bristles 

 are flattened at the tip, and seem specially adapted for this function. 



In the same paper the colouring of this caterpillar is discussed. 

 In its early stages, it is supposed to be imitative of a bird-dropping, 

 but after the last change of skin it becomes conspicuously adorned 

 with warning-colours. Like many other larvae, it hides from its 

 enemies until it is too large to be hidden any longer, and then it tries 

 to frighten them away. 



An important contribution to Insect Embryology has been lately 

 made by Dr. R. Heymons, of Berlin (" Zeitschr. fiir Wissensch. Zoo- 

 logie," vol. liii., p. 434, &c.). This is a paper entitled " Die Entwick- 

 lung der weiblichen Geschlechtsorgane von Phyllodromia (Blatta) 

 gei'inanica, L.," which gives a very exhaustive account of the origin 

 and formation of the ovaries and oviducts in that household pest 

 known as the German Cockroach. This insect is a smaller and paler 

 species than the Common Cockroach [Peyiplaneta oruntalis), which it is 

 said to be supplanting in many places in Britain, where it has suc- 

 ceeded in establishing itself. In his introduction, Dr. Heymons points 

 out that technical difficulties have hitherto prevented a complete study 

 of this subject. The eggs of the cockroach are enclosed in a chitinous 

 capsule, and the yolk-mass contained in each egg is of a nature 

 unfavourable for microscopic investigation of the early stages of 

 development. These obstacles have now, however, been successfully 

 overcome. The cockroach is an insect of a primitive and generalised 

 type, and its development is not complicated by secondary metamor- 

 phic adaptations ; hence it is specially valuable for embryological 

 research. 



The primitive germ-cells arise from the mesoderm, from the 

 ordinary cells of which they may be distinguished by their larger 

 size. They first appear towards the hinder end of the blastoderm, 

 before the formation of the somites. They are also formed, however, 



