218 THE UNIVERSITY SCIENCE BULLETIN. 



of water is kept passing beneath the carapace and over the gills. This 

 water enters the gill chamber from the rear, passing directly by the 

 abdominal pleurites. The current would be strongest at the first ab- 

 dominal pleurite, and it is just here that we find the first eggs. Figure 

 1, plate XXVIII, attempts to illustrate this point. The eggs, therefore, 

 are placed upon the crayfish in the region where there are the best 

 chances for aeration. 



If only crayfish heavily burdened were examined, it would not be so 

 apparent, but even the photographs of the one shown by Doctor Abbott, 

 which must have carried some 3,000 eggs, the back of thorax and ab- 

 domen were comparatively clear. On the other hand, if the oviposition 

 be light, it is obvious at once that there is a choice of position in placing 

 the eggs upon the crayfish, and that this choice is coincident with the 

 region bathed with the freshest water. The crayfish studied were taken 

 from the Griesa Pond on June 15 and 17, and from the Race Track pool, 

 July 5. The series studied by Doctor Abbott were taken early in July 

 and began to hatch the 8th. 



Incubation. No eggs have been observed from oviposition to hatch- 

 ing, but since the eye spots show up about four days before hatching it 

 would indicate that incubation is about the same as with other Corixids. 



Hatching. The process appears to be the same as with other Corixid 

 nymphs studied, the egg splitting back in from six to eight lobes. 



Behavior of Newly Hatched Nymphs. The nymphs, upon hatching, 

 keep close to the bottom and prefer the dark, according to Doctor Abbott. 

 Their safety depends directly, in these early hours, upon inconspicuous- 

 ness brought about by their transparency and tendency to remain quiet. 



Doctor Abbott's specimens were reared in a large zinc-lined aquarium, 

 having a superficial area of 30 to 35 square feet. His attempts in small 

 jars failed. The writer has carried a generation through in a common 

 glass battery jar vidthout attention, the jar being prepared beforehand. 

 While Doctor Abbott noted that mortality was high from third instar 

 on, many being found dead in the morning, when combined with the 

 observation that the nymphs were more active dull dark days, led him 

 to believe they were more active at night. It might be added that there 

 is a possibility that the activity or tendency to come to the surface at 

 such times may be due to the need for air. On bright days the water 

 plants add quantities of oxygen to the water, and it has been observed 

 that they can be forcibly retained submerged in vessels containing water 

 plants for longer periods than in clear water. In boiled water they 

 become distressed rather quickly. 



Number of histars. There are five nymphal instars which have been 

 described by Doctor Abbott. The description of the egg and nymphal 

 stages is taken from his paper. 



DESCRIPTION OF STAGES. 



The Egg. 



"Length about .9 mm. Breadth about .4 mm. Shape elongate-oval, 

 bilaterally rather than axially symmetrical, i e., one side nearly straight, 

 the opposite strongly curved. Colour grayish yellow (later stages only 



