The vertical distribution and swimming ability of the three larval stages (Zoea I, II, and III) of Homarus gammarus were determined in laboratory experiments. In an artificial water column, newly hatched larvae were positively phototactic to white light at intensities near 0.6 mmol m 2 s . The positive phototactic behaviour decreased with increasing larval age and stage. Accordingly, older larv...

THE gregarines of Gammarus pulex L. have long been known, in fact they were some of the earliest of these Sporozoa to be observed (Text-figs. 1-3). However,.so far, no adequate description has been given of the gametes and spores which are the most important stages from the systematic point of view. Lady Muriel Percy, who worked in this Department from 1925 to 1929, helped in the investigation ...