216 THE UNIVERSITY SCIENCE BULLETIN. 



readily recognized by Abbott's description and figures. The dimorphism 

 of the sexes is perhaps the most remarkable in the entire family, the 

 head of the male being decidedly acuminate, while that of the female is 

 normal. See figs. 2 and 3 on plate XXVIII. 



Habitat. This form is found in the muddiest of ponds in the middle 

 west. No waters appear to be too stagnant for its abode, which may 

 account for its strange habit of placing its eggs upon the carapace of 

 crayfish. 



Hibernation. Females of this species have been taken by the writer in 

 Kansas in winter collecting. 



Mating. Mating takes place in the same manner as with other Corixids 

 and at about the same time. 



Oviposition. In a paper entitled "An Unusual Symbiotic Relation be- 

 tween a Water Bug and a Crayfish," Doctor Abbott gives an interesting 

 account of the strange habits of egg deposition of this species. The 

 paper is accompanied by two photographs of crayfish laden with Corixid 

 eggs. He describes the condition very accurately, noting that the re- 

 ception of each egg cup, "as if the affixing of the egg had either softened 

 the chitin somewhat, or had taken place before the hardening subsequent 

 to ecdysis had been completed." 



Forbes, in 1876, seems to have been the first to note that crayfish carry 

 Corixid eggs. He suggested that they were probably the eggs of Corixa 

 alternata Say, but since we know the habits of both species in question, 

 it was without doubt Abbott's Ramphocorixa balanodis. While both Doc- 

 tor Abbott and Doctor Forbes failed to find these eggs anywhere else in 

 the water, the writer has occasionally found them attached to sticks and 

 floating plants, but never in numbers. There is indeed a striking inti- 

 macy between these animals. Doctor Abbott attempts to explain the 

 "symbiosis" as follows: 



"The investiture of eggs commingled with debris certainly renders 

 the crayfish less conspicuous and it probably profits by the arrangement 

 in much the same way as do various shore crabs which are decorated 

 with sponges, algse or coelenterates. Whether the water bug improves 

 its chances against racial extermination by the adoption of such a pug- 

 nacious protector it may be too much to assume, but at any rate, what- 

 ever the utilitarian value of the habit, it must be of the same nature as 

 that which obtains in the widely distributed genus Zaitha." 



In a study of a considerable series of crayfish carrying various num- 

 bers of eggs, the writer believes he has found a plausible explanation 

 for the unique support employed by this Corixid. A casual examination 

 of many Cambarus immunis, together with the tabulation of the distri- 

 bution of eggs upon a representative series, herewith represented, leads 

 to the belief that it is a matter of aeration. 



An examination of the table shows that there was a marked tendency 

 fo." the first eggs to be placed low on the pleurites of the first abdominal 

 segment. That, after many eggs were thus deposited, they were placed 

 upon the carapace near the lower posterior margin. In one case, num- 

 ber 5, there were 13 eggs on top of the carapace behind the eyes. 



When we study the respiration of the crayfish we find that a current 



