268 



SCIENCE 



[N. S. Vol. XXXIII. No. 842 



entire year, and comparisons made with the stock 

 growing in the laboratory. The wheat clearly 

 showed the effect of the different treatments, but 

 aphids did not manifest any significant change. 

 When the sexual and intermediate forms began 

 to appear on the regular stock in October they 

 likewise began to appear on these experimental 

 pots. 



In the woolly aphis the agamic forms were 

 wingless throughout the entire summer season. 

 The first winged forms appeared September 19, 

 and ceased to appear on December 6. The off- 

 spring of these winged forms are the true sexes. 

 The first of these to appear was on December 25. 

 These true sexes are wingless and in accordance 

 with the observations of Von Baehr each female 

 produces but one egg. All colonies do not pro- 

 duce winged forms and hence all colonies do not 

 produce sexual forms. All winged forms of the 

 woolly aphis do not produce offspring. Out of a 

 series of nineteen isolated winged forms only 

 eleven reproduced and these eleven brought forth 

 twenty-seven young composed of twenty-one males 

 and six females. 



Thus far it appears difficult to correlate and 

 establish external conditions which would appear 

 to have a direct bearing on the transition from 

 parthogenesis to gamogenesis in aphids. 



In the two forms studied the sexes appear in 

 the fall of the year and may be spoken of as 

 seasonal. This is true also for a very large num- 

 ber of aphids whose behavior in this respect has 

 been recorded by others. This naturally leads to 

 a careful analysis of the conditions obtained at 

 this period of the year. It is our purpose now 

 to continue these studies throughout the next 

 year, dealing chiefly with the questions of tem- 

 perature and light. 



On a Ca^e of Parasitic Tlwracopagus in a Frog: 

 George Wagnee, University of Wisconsin. 

 An instance of a frog having three extra legs 

 extending from an irregularly shaped bone over- 

 lying the sternum; the case was interpreted as 

 representing what by students of teratology is 

 known as an epigastrius (Schwalbe), or a para- 

 sitic epigastrius (Adami). The case is believed 

 to be the first of its kind reported in an am- 

 phibian. A full account of it will be published 

 later in the Biological Bulletin. 

 The Pomace Fly Bred in the Dark for 67 Genera- 

 tions: Feknandus Payne, University of In- 

 diana. 

 The Proposed Laysan Island Expedition and Ex- 

 hibit: C. C. Ntjtting, University of Iowa. 



The Origin of the Sex-cells in Necturus: Bennet 

 M. Allen, University of Wisconsin. 

 The sex-cells of this amphibian arise from that 

 portion of the mesoderm which lies between the 

 future myotome and the future lateral plate. 

 This anlage was recognized as early in develop-' 

 ment as an early medullary plate stage, owing to 

 the fact that it is noticeably thicker than the 

 lateral plate region lateral to it, and that it is 

 at the same time marked off from the anlage of 

 the mesoblastic somites by a constriction thab 

 indicates the first point of division of the meso- 

 dermal sheet. 



The mesodermal cells show very slight differ- 

 ences at this stage, being equally filled with yolk, 

 and having nuclei in which I, thus far, have been 

 unable to distinguish constant and important dif- 

 ferences, nor has it been possible thus far to 

 differentiate them from the nuclei of the endo- 

 derm. It is just possible that further work may 

 enable me to distinguish them in this and in 

 earlier stages, by the use of special staining 

 methods. 



While the outlines of this sex-cell mass are 

 vague at the outset, they become very clearly 

 defined in later stages, when, first the myotome, 

 and then the lateral plate tissues begin to use up 

 their yolk material, while the sex-cells remain 

 unchanged and do not divide. It then becomes 

 evident that the sex-cell anlagen are continuous 

 in the greater part of their extent, being some- 

 what interrupted only at their cranial and caudal 

 ends. 



At the stage with which this account begins, 

 the WolfiBan ducts have not yet been formed. So 

 soon as they make their appearance, however, 

 they lie immediately above and slightly medial 

 to the sex-cell anlagen. In still later stages, the 

 latter are seen to shift toward the median line. 

 This movement accompanies the growth of the 

 lateral plates and appears to be caused by it. 

 The sex-cell anlagen finally meet in the median 

 line and the mesentery forms beneath them. They 

 then migrate laterally to the anlagen of the sex- 



While it will be seen that this account is quite 

 in agreement with Dustin's account of the origin 

 of the sex-cells in Triton, and consequently at 

 variance with the process described in my paper 

 on the origin of the sex-cells in Rana pipiens, I 

 have nothing whatever to retract from the ob- 

 servations and conclusions expressed in that 

 paper. Repeated study of my old preparations 

 and of many new ones have confirmed their accu- 



