Vol. 17 (1)

July / Julio 1969

CONTENTS / CONTENIDOS

A review of the immunology of parasitic nematodes
Valdivieso, D. & J.R. Tamsitt

A contribution to the morphology of the eggs and nymphal stages of Porocephalus stilesi Sambon, 1910 and Porocephalus clavatus (Wyman, 1847) Sambon, 1910   (Pentastomida)
Vargas, V.M.

A double metacercarial infection in an Indian fresh water fish, Heteropneustis fossilis (Bloch)
Chakrabarti, K.K.

Notas sobre la historia natural de la serpiente de los pantanos, Tretanorhinus  nigroluteus
Villa, J.

Contribuciones a la Pteridología costarricense. I. Nuevas especies
Gómez P., L.D.

Report of the chromosome numbers of some Costa Rican anurans
León, P.E.

Studies on the pulmonary surface- active lipoprotein. I.Isolation and chemical characterization of its constituents
Jiménez, J.M.