ANATOMY OF MONOPYLIDIUM PASSERINUM, FUHR. 411 



The fertilised eggs come to lie in the parenchyma behind 

 the female complex in the region formerly occupied by the 

 testes. There are two shells present, the outer being 

 about 0*05 mm. and the inner 0*04 mm. in diameter. The 

 oncospheres are approximately 0*024 mm. long, the 

 embryonal hooklets being 0*012 mm. in length. The polar 

 thickenings mentioned by Prof. Fuhrmann as being present 

 on the embryonic membrane, were seen quite distinctly as 

 deeply staining elliptical structures. 



From the foregoing description, it will be noticed that 

 the main differences from Fuhrmann's account are in regard 

 to the female complex. 



The genus Monopylidium, Fuhrm., was erected in 1899 1 

 for the reception of Davainea ? musculosa, Fuhrm. In 1908 2 

 a diagnosis of the genus was given, stating that there is a 

 simple circlet of hooks. In M. passerinum, Fuhrm., there 

 is a double row, and since this species has been placed by 

 Fuhrmann in his genus, the generic diagnosis will need to 

 be modified in regard to the rostellar armature. The 

 members of the genus may thus possess a single or a double 

 series of hooks. 



Explanation of Plate XVIII. 



Fig. 1. Scolex with rostellum protracted 

 „ 2. Segment, showing genitalia, etc. (dorsal view). 

 ,, 3 Female genitalia seen from the dorsal side. 

 ,, 4. Transverse section of midregion of segment. 



5) 



5. Hook. 



Explanation of lettering : — c, cirrus ; c.s., cirrus sac ; cu., 

 cuticle ; c.p., cortical parenchyma ; d.e.v., dorsal excretory vessel: 

 f.d,, fertilising duet ; g.c, genital cloaca; h., hook; l.m., longi- 

 tudinal muscle; m., medulla; n., longitudinal nerve; o.o?., oviduct; 

 ov , ovary; ov.br., ovarian bridge; r, rostellum; r.m., rostellar 

 muscles; r.s., receptaculum seminis; s., sucker; s.c.c, subcuticular 

 cells; s.g., shell gland; t., testis; tr. e.v., transverse excretory 

 vessel; v., vitelline duct; va,, vagina; v.d., vas deferens; v.e.v., 

 ventral excretory vessel; v.g., vitelline gland. 



1 Fuhrmann, Centrb. Bact. Orig. I, xxvi, 1899, p. 622-7. 

 ■ Fuhrmann, Zool. Jahrb., Supp. Bd. x, i. 1908, p. 65. 



