476 



SCIENCE 



[N. S. Vol. XXXI. No. 795 



the higher intensity and the positive to the lower 

 intensity. When thus made negative to dim light 

 Orchestia becomes again positive if exposed to 

 strong light. Kept in dry air, the animals become 

 negative. After retention in darkness they are 

 positive. Placed in water they are negative. 



A number of these reactions are of evident im- 

 portance in the animal's daily movements. The 

 reversal from positive to negative with decrease 

 in illumination aids in directing the animal's 

 movements in reentering the eel grass, as likewise 

 does the negative reaction when becoming too dry. 

 The animal's negativity when in water aids it in 

 reaching shore when overtaken by the tide, the 

 shore line serving as a dark region as compared 

 with the equally illuminated expanse of water in 

 all other directions. 



On the Transition from Parthenogenesis to Oamo- 



genesis in Aphids and Braconids : S. J. Hunter, 



University of Kansas. 



Continuous experimental study since May, 1907, 

 on the aphid, Toxoptera graminum, has brought 

 out the following regarding the development of 

 aphids as illustrated by this species: 



Parthenogenetic forms appear during the spring, 

 summer and early fall. These forms may be 

 winged or wingless, the latter greatly predom- 

 inating. The characters of each remain constant 

 until about October 1, when, as first observed by 

 Glenn in this laboratory, these parthenogenetic 

 forms begin to produce intermediate forms vary- 

 ing in structure between the winged partheno- 

 genetic form and true female on the one side and 

 the wingless parthenogenetic form and true female 

 on the other aide. Within the bodies of these 

 intermediate forms appear, in some live young, in 

 others winter eggs, in still others both winter 

 eggs and living young. All such intermediate 

 forms, however, die without producing offspring 

 or eggs, as do many of the apterous partheno- 

 genetic individuals belonging to the sexual gen- 

 eration. 



These intermediate forms seem to be partheno- 

 genetic individuals affected by the stimuli which 

 bring about the transition from parthenogenetic 

 females to the true sexes. In some the repro- 

 ductive organs are unmodified, in others they ap- 

 proach the true female type to a greater or less 

 degree. These intermediate forms belong to the 

 sexual generation and may be considered as an 

 attempt toward the development of the sex indi- 

 vidual. They play no part in the life of the insect. 



The parent of these intermediate forms and of 



the true female may be either winged or wingless. 

 The males have no intermediate forms and are 

 uniformly the offspring of the wingless partheno- 

 genetic females. One single parthenogenetic wing- 

 less individual has been observed to produce types 

 of all the above described forms. The above inter- 

 mediate forms together with the appearance of 

 the true sexes occur only during October, Novem- 

 ber and December regardless of the conditions 

 under which the various experimental stocks are 

 kept throughout the year and without reference 

 to the number of generations. 



Young growing wheat has been the uniform 

 food plant throughout the entire period of experi- 

 mentation. 



In the braconid, Lysiphlehus tritioi, a parasite 

 of T. graminum, gamogenesis occurs in nature. In 

 one count of a thousand insects taken in the field 

 5 per cent, were males, in another 35 per cent. By 

 isolation of virgin females in fourteen experiments 

 all offspring were males, and in seven experiments 

 1 out of 26, 4 out of 27, 3 out of 17, 1 out of 22, 

 I out of 18, 1 out of 12, 2 out of 27 were females, 

 making a total for the twenty-one experiments 

 of 339 males and 13 females. In an extensive 

 series of subsequent experiments no females have 

 appeared. Of these parthenogenetic forms it is 

 worthy of note that 203 of the males had 15- 

 jointed antennae, 131 had 14-jointed antennae and 

 5 had 10-jointed antennae. Of the 13 females, 8 

 had I3-jointed antennae and 5 had 12-jointed an- 

 tenna. Gamic females show the same conditions, 

 but among gamic males no I6-jointed forms have 

 been found. Polyembryony does not occur in this 

 parasite. 



Proliferation of Eyes in an Abnormal Tentacle 

 of a New Species of Marine Oasteropod: F. N. 

 Baich. (Introduced by G. H. Parker.) 

 In the unique specimen of Onohidiopsis corys 

 sp. nov. the left tentacle is bifid, the internal, or 

 mediad, member appearing nearly normal and 

 bearing a normal eye. The external member is 

 abnormal in size and shape, ig folded backward, 

 bears on the surface thus exposed {but morpho- 

 logically mediad) a normal-appearing eye, and if 

 folded forward into its true morphological posi- 

 tion would be the mirror-image of the internal 

 member. On sectioning, the bifid tentacle is seen 

 to bear two encysted parasites, probably cercarian. 

 The " eye " in the external member is seen to 

 consist of a group of four eyes apparently prolif- 

 erating one from another and constituting one 

 series of three " generations," and another junior 



