147] LIFE HISTORY OF GORDIUS AND PARAGORDIUS—MA Y 27 



grass over the water they do not hesitate in the least to drop down into the 

 water and are in no haste to get back to land. On cloudy days the speci- 

 mens often remain at the bottom of the grass and can not be obtained at 

 all, but on bright days, when it is just cloudy enough for the sun to be shaded, 

 many of them come up and are easily obtained because they are less active 

 than on sunny days. I have been able to obtain them most easily at twi- 

 light just after sunset. At that time they come out on the grass and weeds 

 and do not easily become aware of approach, and even when disturbed 

 they often merely run along to a new position without making any serious 

 attempt to escape. 



The larvae at first penetrate the adipose tissues of the hosts, making 

 their way not only between the cells but also thru them (Figs. 47, 54). 



In later stages they come to lie free in the body cavity of the host 

 (Fig. 55). There is usually a difference in the location in the host between 

 the Mermithidae and Gordiacea. While the Gordiacea occupy exclusively 

 the body cavity, the Mermithidae usually penetrate the tissues surrounding 

 the body cavity and sew themselves thru between the muscle bundles of 

 the thorax. Whenever Gordius becomes too crowded in the abdominal 

 cavity and is forced into the thorax it passes between the alimentary canal 

 and the thoracic muscles, but never between the muscle bundles. 



The parasite does not appear to impair very greatly the health of the 

 host, for, unless the infection is very heavy, the infected specimens appear 

 to be just as active as those that are not infected. In this respect the infec- 

 tion differs from an infection with Mermis. I have several times found 

 specimens infected with Mermithidae to be sluggish. 



Observations made during 1914 seemed to indicate that the infection 

 was confined to the females and that the parasites prevented the develop- 

 ment of the ova. No attention was paid to the sexes of the hosts during the 

 early part of the season, but during October only females were found to be 

 infected. 



During the infection experiments in 1916 it became evident that males 

 as well as females became infected, and later when hosts were collected in 

 the field for examination males were found to be almost as heavily infected 

 as females. Of 711 males examined 64 or 9 per cent were infected and 

 of 440 females examined 59 or 14 per cent were infected. Of the infected 

 females many had eggs, but usually the number of eggs was smaller than 

 in normal females, and in heavy infections with older worms there were 

 usually no eggs present. In males no effect on the reproductive organs 

 was noted, perhaps mainly because it is more difficult to detect a diminu- 

 tion of the testes than of the ovaries. 



The records of 1914 showing no infection in males remained a puzzle 

 until a collection was made on October 14. Of 10 males collected not one 

 was infected, while in 11 females seven were infected. It is probable, then, 



