300 ENTOMOLOGICAL NEWS. [July, '17 



as long as the abdomen, which has 7 and one genital segments. The 

 prothorax is distinct. 



Varying from 3 to 5 days, the bug molts for the second time. 



Third Instar. The antennae continue to change. The 4th joint is 

 still the longest, 3 the shortest, followed by 2 and i in the order given. 

 The eyes are reniform. In the legs, the femora are longer than the 

 tibiae in the ist and 3rd pairs, and subequal in the second. The abdo- 

 men is longer and the legs appear set less far back. In other respects 

 there are no perceptible changes. 



The third molt follows the second in 3 to 6 days. 



Fourth Instar. In this instar the antennae continue to change, and 

 the differences in length are not so great; joint 4 is still the longest, 

 but 2 and 3 are subequal and the shortest, i being not greatly shorter 

 than 4. The femur and tibia of the anterior legs are subequal; and 

 the femur is longer in the 2d and 3d pairs. The hind femora have dark 

 spots from which arise long setae. The abdomen has further increased 

 in length, the segments being wider and more distinct. Joint 3 of the 

 rostrum is the longest, 2 is the shortest and 4 is as before, and nearly 

 equal to i. All tibiae have combs and all claws are simple. 



The fifth instar is reached in 3 to 5 days. 



Fifth Instar. In this instar the form and general appearance of the 

 nymph begin to approach more closely to the adult. The head is rounded 

 and set with long setae, the eyes are reniform. In the antennae joints 

 I and 4 are subequal, and longer than 2 and 3, which are also subequal. 

 The chief antennal difference is at the base of the third antennal joint 

 which has a pedicellate appearance. The rostrum is the same as before, 

 except that the 3d joint is much longer in proportion. The prothorax 

 is differentiated and the mesothorax distinct, with a minute scutellum. 

 The wing-pads are notable and reach half-way to the 4th abdominal 

 segment. The legs are as before, with thicker femora than tibiae. The 

 second and third femora have the dark setigerous spots, and the third 

 in addition is set with spines. The middle tarsi are much elongate, and 

 all the tarsi continue single-jointed. Abdominal segments are very dis- 

 tinct and the two genital segments very prominent. In the cast skin 

 two long slit-like spiracles are seen in the mesothorax in front of the 

 intermediate coxae. 



In five to seven days the little bug molts for the fifth and last time, 

 and reaches the adult. The chief changes in structure in the external 

 skeleton are the two-jointed tarsi, the node at the base of the third 

 joint of the antennae, the much larger eyes in comparison to the head 

 and the prothorax and mesothorax fused together. 



The entire internal anatomy of Gerris marginatus is still to be 

 worked out, and the external organs of respiration as well. 



