ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 711 



be used. Temperature is the most important factor in development, a 

 high temperature accelerating it. Other factors are the nature of the 

 food, and moisture, and the author indicates the effect of these. Fermen- 

 tation is also an important factor. The shortest time occupied in 

 development, that is, from the deposition of the egg to the exclusion of 

 the imago, is eight days, but this period is only attained at a constant 

 temperature of 35° C. : under unfavourable conditions the development 

 may extend over several weeks. There are three larval stages, and the 

 shortest times for the development of each stage is : egg, from deposition 

 to hatching, 8 hours ; first larval instar, 20 hours ; second larval instar, 

 24 hours : third larval instar, 3 days ; pupal stage, 3 days. House-flies 

 breed from June to October, but if the necessary conditions of tempera- 

 ture and suitable food are present, they are able to breed practically all 

 the year round : these conditions are not, as a rule, satisfied in winter, 

 except in such places as warm stables, etc. The flies become sexually 

 mature in ten to fourteen days after emergence from the pupa, and they 

 may begin to deposit their eggs as early as the fourteenth day after 

 emergence. Each fly lays from 120-150 eggs in a single batch, and it 

 may lay as many as six batches during its life. 



The second part of the paper deals with the structure of the mature 

 larva. The body is composed of thirteen segments, including the 

 remnant of the cephalic region, or " pseudocephalon." The apparently 

 single second segment the author regards *as of a double nature. The 

 muscular system is described in detail, and the series of muscular 

 actions which probably takes place during locomotion is discussed. The 

 only sensory organs are two pairs of tubercles situated on the dorsal 

 sides of the oral lobes. By their structure they indicate an optical 

 function. The alimentary tract is very long, and consists of pharynx, 

 oesophagus, proventriculus, ventriculus, intestine, and rectum. In addition 

 to a pair of salivary glands, whose ducts unite to form a single duct 

 opening at the anterior end of the pharynx, and a pair of bifurcating 

 Malpighian tubes, the larva possesses four caeca at the anterior end of 

 the much-convoluted ventriculus. The tracheal system, the vascular 

 system, and the imaginal disca are also fully described. 



Protandry in Insects.* — R. Denioll discusses the meaning of the 

 protandry of bees and other insects. There may be difference of a 

 month between the appearance of the males and the appearance of the 

 females. He thinks that the males are thereby subjected to a process 

 of selection. Good nutrition for several weeks will have an important 

 influence in the struggle for the females. The older males have the 

 most efficient mouth-parts, and they tend to reproduce sooner and with 

 more result than those less well-equipped. Thus the mouth-parts of 

 the females, which are all-important, are improved by the paternal 

 inheritance. 



Gastrophilus Larvae in Human Skin.f — N. Cholodkovsky calls 

 attention to more than one case of the occurrence of larvae of Gastro- 

 philus (G.jjecorum Fabr. or O. hcemorrhoidalis L.) burrowing in the 

 human skin, and causing " creeping disease." 



* Zool. Jahrb., xxvi. (1908) pp. 620-8. 



t Zool. Anzeig., xxxiii. (1908) pp. 409-13 (2 figs.). 



