Studies from the Biological Laboratory

animal anus appearance become blastopore body branchiæ central cells changes cilia curve diameters digestive cavity digestive tract discharge dorsal surface early stages ectoderm embryo endoderm experiments fluid food yolk foot formative pole frog Gasteropods gastrula germinative vesicle gills gland glottis granular hyphæ increase interval of stimulation invagination irritation Lamellibranchs Lankester layer lever limb lumbar vertebræ lungs macromere male mass membrane mesoderm millimetre minutes later Molluscs nearly nerve normal nutritive pole observations opening optic lobes ovoid cells oyster period of activity period of rest planula Plate polar globule portion position posterior Rabl Ray Lankester respirations respiratory centre respiratory movements rhythmic sciatic second micromere seen segmentation cavity shell shew shown in Figure side single contraction spherules sphincter sporangia spores stage shown stomach summation sweat temperature tetanic throat movements throat retraction tion tracing transparent velum ventral surface W. K. BROOKS