A SURVEY OF THE HOLARCTIC LINYPHIIDAE （ARANEAE）, OF THE ERIGONINE GENUS ZORNELLA JACKSON, 1932

The Holarctic erigonid genus Zornella has been surveyed. Four spedes are recognized in this genus, two Palaearctic： Z. aultrigera （L. Koch, 11879） ＆ Z. orientalis sp. nov., and two Nearcfic： Z. arrnata （Banks, 1906） ＆ Z. ayptodon Chamherlin, 1920. It is demouslrated that neither nearcfic species is agnspedtic with Z. atltrigera as was thought by Holm and other authors. Z. sp. nov. is describcd from northeastern Siberia. All of the species are illustrated and their distributions mapped.     

THE RATE OF TRANSMISSION IN THE NERVE NET OF THE C?LENTERATES

Nerve net transmission in Metridium at 21°C. varies from 121 to 146 mm. per second.     

TEMPERATURE COEFFICIENT OF THE ACTION OF β-RAYS UPON THE EGG OF NEREIS

The temperature coefficient of the action of β-rays from radium upon the egg of Nereis lies between 1.1 and 1.2. This is of a magnitude characteristic of photochemical reactions.     

METAMORPHOSIS OF THE LARVA OF THE POLYCHAETE ARENICOLA CRISTATA. MORPHOLOGY OF THE ‘HOUR-GLASS’ STAGE

The constricted ‘waist’ of the metamorphosing larva of the polychaete Arenicola cristata is described, using light and electron microscopy. The constriction is shown to be the consequence of the discharge and collapse of a post-trochal ring of epithelial cells which remain as functional components of the post-metamorphic juvenile. Morphological differentiation of neuro-effector and interneuronal contacts is initiated at this time. Muscular and neural changes are discussed in terms of their role in effecting metamorphosis.