192 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I4I 



pulchrum (Schell, 1952a) ; in the latter species the deposit eventually 

 completely surrounded the nematode larva which was killed and 

 "chitinized." Apparently these pigmented cysts surround unhealthy 

 or dead larvae and are secreted as a defensive mechanism by the host 

 (Schell, 1952a). Oswald (1958) has reported finding similar pig- 

 mented cysts in Blatta orientaUs and Periplaneta americana that were 

 experimentally infected with Rictiilaria coloradensis. 



Our classification of the helminths follows Hyman (1951, 1951a). 



HELMINTHS FOR WHICH COCKROACHES SERVE AS 

 PRIMARY HOSTS 



Phylum ASCHELMINTHES 



Class NEMATODA 



Order MERMITHOIDEA 



Family MERMITHIDAE 



Undetermined mermithids 



Natural hosts. — Ectobius pallidus, U.S.A., Plymouth, Massachu- 

 setts (Roth and Willis, 1957) : This mermithid lies coiled in the body 

 cavity of the host and one end may extend into the thorax. Ap- 

 parently, the host is eventually killed and the worms may leave the 

 cockroach ventrally between the thorax and abdomen (pi. 29, A) or 

 thorax and head. 



Periplaneta americana, Germany (Bode, 1936) : Attacked by 

 "Mermis" or "Gordius." It has been suggested that the name Mermis 

 is often applied without critical identification to immature Nematoda 

 found in insects (Buxton, 1955). 



Order RHABDITOIDEA 



Family DIPLOGASTERIDAE 



Diplogaster sp. 



Synonymy. — Lycolaimus [Goodey, 1951]. 



Experimental host. — Blattella germanica, U.S.A. (Christie and 

 Grossman, 1933). 



Family STEINERNEMATIDAE 



Neoaplectana sp. 



Experimental hosts. — Blattella germanica, Nauphoeta cinerea, and 

 Periplaneta americana. U.S.A. (Dutky and Hough, 1955) : This 

 nematode, found in codling moth larvae, is close to Neoaplectana 



