hravssei (Steiiier, 1923), found in the intestine of the wasp, 

 Cephalcia abictis (L.), is so closely related to the genua Neo- 

 aplectana that a similar mode of life is suggested but verify- 

 ing information is lacking. 



Among the rather numerous and diverse nematodes that have 

 been reported from snails and slugs are representatives of the 

 Angiostomatidae and Cosmoeercidae, two families that include 

 also parasites of Amphibia. The four species mentioned below 

 will serve as examples but very little information is available 

 about life cycles. Angiostoma limacis belongs to the Angiosto- 

 matidae while the other three, according to Chitwood and Chit- 

 wood (1937), probably belong to the Cosmoeercidae. 



Angiosioma limacis Dujardin, 184.5, has, on at least two oc- 

 casions, been found in the intestine of Arion ater (L.) (Syn. 

 Limax rufa) where, apparently, it reaches maturity. Chitwood 

 and Chitwood (1937) report finding a very closely related spe- 

 cies in the intestine of a salamander, Plctliodon cinerens. 



Ascaroides limacis Barthelemy, 18.38, was found in eggs of 

 Deroceras agrestis var. cincracea Moq. Tand. (Syn. Limax 

 griseas), each infected egg containing one to four larval para- 

 sites. Barthelemy (18.">6) determined that the nematodes were 

 already present when the eggs were deposited. Apparently the 

 adult of this parasite has not j'et been studied. 



"Angiostoma" helicis Conte and Bonnet, 1903, was secured 

 by its discoverers from the slug, Helix aspersa (Miill.), where 

 it occurred in the genital organs, especially the oviducts and 

 seminal vesicle, but not elsewhere in the body. Conte and Bon- 

 net (1903) concluded that the parasite is passed from host to 

 host during copulation. 



Trionchonema riisticum Kreis, 1932, was secured from the 

 land snail, Folygyra espwola Bland. Presumably this parasite 

 is an inhabitant of the alimentary tract though the location 

 \\-ithin the host was not specified. Kreis (1932) refers to the 

 development of a "filariform" larva and suggests the possibil- 

 ity "that there is still another stage of development, perhaps 

 a rhabditiform larva, which could not be found and which may 

 perhaps be free-living. ' ' 



Parasites of the Alimentary Tract 



All nematodes belonging to the families Thelastomatidae and 

 Rhigonematidae and to the subfamily Ransomnematinae are 

 parasites of the alimentary tract and one finds an occasional 

 species of the family Diplogasteridae that has acquired this 

 mode of life. 



The thelastomatids are parasites of insects and myriapods and 

 scattered through the literature are descriptions of between 60 

 and 70 species but usually not much other information. How- 

 ever, studies by Galeb (1878), Dobrovolny and Ackert (1934), 

 and others indicate that most of these species probably have 

 about the same tj-pe of life cycle and that it is comparatively 

 simple. Eggs pass out of the host with the feces. Eggs do not 

 hatch in the intestine to reinfect the same host but must first 

 undergo some development on the outside to reach an infective 

 stage. The various arthropod hosts acquire their parasites by 

 swallowing these infective eggs. 



In the genus Pseudonymous, the species of which are parasites 

 of aquatic beetles, the egg is provided with two entangling ap- 

 pendages, the so-called spiral filament (Fig. 13.") R, p. 176) 

 which, presumably, enables the egg to hang on aquatic vegeta- 

 tion thus increasing its chance of lieing ingested. From two to 

 four eggs of Biiicma biiirma and B. ornaia (Fig. 166G) are en- 

 closed in an outer capsule or case of loose texture formed, ap- 

 parently, by the entangling and anastomosing of polar fila- 

 ments. The purpose of this adaptation is obscure. 



The Rhigonematidae and Ransomnematinae are small groups 

 with only a few species each. It seems proliable that life cycles 

 of these nematodes are not materially different from the type 

 of life cycle characteristic of many thelastomatids though, ad- 

 mittedly, such a statement is wholly conjectural. 



Cephalobium microbivorum Cobb, 1920, a member of the 

 Diplogasteridae, inhabits the intestine of the black field cricket, 

 Gryllns assimilis (Fab.), Avliere it may occur in numbers up to 

 30 or more. Infected crickets have been collected in Virginia 

 and Kansas. In the region of Manhattan, Kansas, according 

 to Ackert and Wadley (1921), there are two races of this in- 

 sect each having one brood a year. One race matures during 

 April and May and overwinters in the nymph stage while the 

 other race matures during August and September and over- 

 winters in the egg stage. These investigators found that in 

 autumn over 85 per cent of the adults of the latter generation 

 were infected, the incidence being somewhat higher in female 

 (about 90 percent) than in male crickets (about 70 percent). 



Eggs of C. microbivorum are usually deposited in a four-cell 

 stage and pass out of the host with the feces. Ackert and Wad- 

 ley concluded that probably eggs hatch after being voided and 

 that a cricket becomes infected by ingesting larval nematodes 



perhaps after these have undergone a brief period of free-living 

 development. The two races of crickets provide the parasite 

 with suitable hosts throughout most of the year and, no doubt, 

 some of the nematodes pass the cold season in overwintering 

 nymphs. The presence of this nematode has no obvious effect 

 on the well-being of the cricket. 



Leidynema appendiculatum (Leidy, 18.50) Chitwood, 1932. 

 — The life history of Leidynema appendiculatum, which was in- 

 vestigated by Dobrovolny and Ackert (1934), is probably more 

 or less typical of many thelastomatids and will serve as an 

 example of the family. This nematode is a parasite of the 

 cockroaches, Blatta orientalis (L.) and Feriplaneta americana 

 (L.). Out of 259 individuals of P. americana collected by 

 Dobrovolny and Ackert at Manhattan, Kansas, 90 harbored this 

 parasite in numbers of from 1 to 36 per host. 



The egg, deposited in a one to a four-cell stage, passes out 

 of the insect with the feces. After extrusion it undergoes a 

 short period of development and a tadpole-like larva (Fig. 

 166 A) is formed. The larva is at first motile, wiggling and 

 squirming about, but becomes inactive as the infective stage 

 (Fig. 166 B) is reached. Dobrovolny and Ackert found that 

 at 37° C. eggs reach this infective stage in 3 to 7 days and 



Fig. 166. PARASITES OF THE INTESTINE 



A-F — Leidynema appendiculatum (A — -Egg with active embryo; B — 

 Egg with larva in resting stage; C — An early stage larva, presumably 

 second stage; D — Larval female showing intestinal diverticulum be- 

 ginning to form; E — Adult male; F — Adult female). G — Binema or- 

 naia, egg capsule. A-P, after Dobrovolny and Ackert, 1934. 



250 



