294 SUMMARY OF CURRENT RESEARCHES RELATING TO 



increased the mean number of facets from 98 '0 to 189 "5. Three 

 similar selections for low numbers decreased the mean from 98 '0 to 

 83-7. The lowest individual (89-0) in the "high" hnes after three 

 selections is higher than the mean of the " low " strains, and the highest 

 individual (137 "0) of the "low" strains is lower than the mean of the 

 "high" strains. Significant progress was noted in each of the three 

 selections in both " liigh " and " low " lines. There are some differences 

 in variability in the different generations, but no significant change 

 was proved. Regression towards the mean of the general unselected 

 population decreases with successive selections. Regression towards the 

 mean of the parental populations increases with successive selections. 

 This increase makes it improbable that " bar-eye " stock can be raised 

 to the original level by continued selection. 



The authors consider that these data show that individuals in any 

 generation differ as regards germinal constitution. If this difference 

 in germinal constitution is solely in the unit factor concerned in 

 "barring," then variability in this unit factor must be assumed. It 

 is, however, more probable that there are other factors concerned in 

 facet number. In that case the selection effect may be due either to 

 variability of single unit factors or to original differences in factorial 

 composition. That it is due in part at least to the latter is indicated 

 by the increase in regression towards the mean of the parental generation 

 with successive selections. 



Housefly as Carrier of Helminth Ova.* — T, 0. Shircore reports on 

 an examination of houseflies about the Native Hospital at Mombasa, 

 the result of which was to show that some harboured ova of Tricho- 

 cephalus cUsjmr, Anki/Iostomum duodenale^ Ascaris lumbricoides, Schisto- 

 somum mansoni, and Taenia saginata. 



Experiments on Eg-gs of Beetles.f — R. W. Hegner has experi- 

 mented with the eggs of the potato-beetle {Leptinotarsa decemlineata) 

 and the willow-beetles {Calligrapha multipunctata and C. bigshyana) in 

 order to determine the role of the cytoplasm in development. The 

 beetle's egg consists of a large central mass of yolk surrounded by a 

 thin superficial layer of cytoplasm. The maturation divisions take place 

 in the cytoplasm near one side. The female pronucleus, surrounded by 

 a small amount of cytoplasm, then moves towards the centre of the 

 yolk-mass, forming a sort of minute island. Here the male pronucleus 

 unites with it, and the first cleavage divisions occur. The cleavage 

 nuclei migrate towards the periphery as they increase in number, finally 

 fusing with the superficial layer of cytoplasm. The blastoderm of a 

 single layer of cells is thus formed. The visible substances within a 

 freshly laid Qg^ are (1) the superficial layer of cytoplasm, (2) yolk- 

 globules of various sizes, (3) the male and female pronuclei, and (4) a 

 mass of granules near the posterior end which take part in the formation 

 of the primordial germ-cells. These granules are called by Hegner the 

 "germ-track determinants." When the egg is centrifuged a "grey- 



• Parasitology, viii. (1916) pp. 239-43. 



t Reprinted from 16th Rep. Michigan Acad. Sci., 1915, pp. 49-54 (9 figs.). 



