LIFE-HISTORY OF THE GENUS MERMIS. 333 



ground, and if they can bear desiccation without loss of vitality — which 

 is by no means improbable, as some minute animalcules are well known 

 to possess this i)roperty — the other conjectures are warranted, for most 

 of the Orthoptera infested by hair- worms are fond of drinking from raia 

 or dew-drops. The life of these minute creatures is devious and preca- 

 rious, and but an extremely small proportion of those that are born will, 

 under the circumstances we have imagined, be fortunate enough to meet 

 with all the requisitions to successful development; but there is due 

 provision for the perpetuation of the species, through all such vicissi- 

 tudes, in any animal so enormously fecund as to bring forth nearly seven 

 million eggs. 



The hair-worms belonging to the genus Mermis have a different ana- 

 tomical structure, and a quite different life-history. from those belong- 

 ing to the genus Gordius. Siebold ^^ found Mermis albicans plentifully 

 investing the larva of a little white moth with black spots [Yponomeuta 

 cognatella, Hiibn.), which larva feeds gregariously on Uvonymus euro- 

 pceus. He also caused them to infest other Lepidopterous larvce, as 

 of Pontia, Gastropaclia, &c. The Mermis acquires full growth within 

 its host, and then forsakes it by boring out with the head. All the 

 specimens so leaving their victim are sexless, and are characterized 

 by a mouth consisting of a very small aperture at anterior end, and by 

 a minute anal point, which is usually curved.^' Unless they are full 

 grown when the host perishes, or unless they reach moist earth, these 

 asexual worms perish, but if full grown, and they succeed in reaching 

 the surface of moist ground, they at once bore into it, ajid bury them- 

 selves out of sight. Here the sexual organs are developed from a fatty 

 body that the parasitic form contains, and after undergoing one molt 

 the perfect and sexed form is assumed, and the anal end becomes 

 rounded and loses the minute point. During this underground life, no 

 food seems to be required, though several months elapse, and the win- 

 ter is passed before the animal procreates. The female sexual organs 

 are in the middle of the body, ending externally in a slightly swollen, 

 transverse slit. The male genitals are near the end of the body.^^ The 

 sexes unite in knots, and the female lays her eggs in the ground. The 

 young, which are filiform, like the parent, at once worm themselves to 

 the surface, and enter, as parasites, various soft insects, and mostly 

 those that are found under leaves, moss, &c., near the ground. 



From the above brief summary of the life-history of Mermis, it is much 

 easier to understand how they come to infest our locusts. Yet even 

 here we are somewhat puzzled to explain the manner in which tree- 

 inhabiting and even fruit-inhabiting larvte'^^ become infested. Siebold 



seZeitschrift fiir Wis. Zool., v, p. 202. Also Ent. Zeitung (Stettin), 1848, p. 292 ; 1850, p. 329. 



8^ An elaborate and admirably illustrated account of the Anatomy and Physiology of Mermis albicans, 

 by Dr. Georg Meissner, may be found in Zeit. fiir Wiss. Zool., v, 1*854, p. 207. 



88 As Meissner has shown, there are sexual individuals Tvhich iu structure seem to approach herma- 

 phroditism, i. e., true females Tvith many of the male external characters. 



^Mermis acuminata (Siebold), as -we have seen in the note to page 327, infests the larva of Carpocapsa 

 pomonella, which hatches from an egg deposited on the hanging apple, and lives within the apple from 

 the time of its birth till it attains full growth. It has been commonly found infestins the Apple-worm 

 in Europe and of late years in this country. See 5th Mo. Ent. Kep., 1872: Ann. liep/lsr. Y. State Mus. 

 Nat. Hist., 1878. 



