PARASITES 



365 



tance in laboratory mice. Only those which occur commonly or have 

 received special attention in the held of experimentation are described here. 



Syphacia obvelata (rudolphi, 1802). — Also known as Oxyiiris obvelata. 

 The caecum of the laboratory mouse is commonly infected with this small 

 oxyurid (Fig. 147) which may also occur in the colon. Upon special 

 examination of the caecae of 34 experimental mice, J. M. Twort and C. C. 

 Twort (39) found 17 infected with this species, while 

 of the colons of 57 of their animals 9 were found to 

 be infected. 



Description of the genus, for which S. obvelata is 

 the type species, is given by York and Maplestone 

 (46) as follows: "]Mouth bounded by three lips; 

 small cervical alae present; vestibule absent; 

 oesophagus club-shaped with a posterior bulb con- 

 taining a valvular apparatus and separated from the 

 rest by a constriction. Male: with 2 or 3 cuticular 

 ''mamelons" on the ventral surface; posterior 

 extremity bent ventrally, body cut away ventrally 

 behind the cloaca and then suddenly narrows and 

 ends in a long pointed tail; narrow caudal alae 

 present limited to the first part of the tail; two pairs 

 of preanal papillae and one pair of postanal 

 pedunculated papillae supporting the alae behind; 

 spicule relatively long and very obvious; guber- 

 naculum directed transversely. Female: tail long 

 and pointed; vulva in the anterior region of the 

 body, behind the excretory pore, and communicat- 

 ing by a short vagina, frequently protruded, with a 

 cuticle-lined ovejector remarkable for the thickness 

 of its muscle coat; uterus single, very long; receptacula seminis parallel and 

 narrow; two ovaries. Oviparous." 



Measurements given for S. obvelata are: male 1.3 mm., female 3.5 to 5.7 

 mm., eggs 10 ^t to 142 jj. in length and 30 /j. to 40 jjl in breadth. 



Not much inflammatory reaction is caused by this parasite unless it 

 occurs in large numbers; and if general hygenic conditions are maintained for 

 the laboratory animals, it is doubtful if heavy infection will occur. 



Aspicularis tetraptera (xitzsch, 182 i). — Also known as Oxyuris tetrap- 

 tera. A . tetraptera like S. obvelata is very commonly found in the intestine of 

 the laboratory mouse, but while 5". obvelata tends to be more limited to the 



Fig. 146. — Cysticer- 

 coid of Hymenolepis di- 

 mi)uita. {From Augus- 

 tine.) 



