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SynopsisThe adaptive character and possible course of evolution—following permanent byssal attachment—of the heteromyarian form in the Bivalvia is considered in relation to the eulamellibranch Dreissenacea and the filibranch Mytilacea. In both it assumes the extreme condition of ventral (anterior) flattening representing a high degree of adaptation for epifaunal life. The presence of a shell shelf in the umbonal regions of Dreissena and Septifer is associated with the greatest degree of ventral flattening; it permits retention of the anterior adductor and its attachment to parallel surfaces. Enlargement of the posterior regions of the visceropedal mass and the posterior territory of the mantle/shell involves formation of an elongated opisthodetic ligament. That of the Dreissenacea, here initially described, is of unique complication. In primitive infaunal isomyarians an organ of locomotion through soft substrates, in these heteromyarians the foot becomes essentially concerned with byssal attachment with which much the greatest part of the small anterior and large posterior retractors becomes exclusively concerned. Although strikingly similar to the Mytilacea, the Dreissenacea which now inhabit slowly moving or still, silt-laden freshwaters would seem most probably to have evolved under very different marine conditions prior to their relatively recent migration into freshwaters.

A description is given of those nerves which arise from the mesothoracic ganglion of Locusta migratoria migratorioides R. & F. There are six pairs of nerves, of which the sixth and most posterior are referred to as recurrent nerves since they join the first nerve of the ganglion in the metathorax. The median nerve is also described. The posterior median nerve of the prothoracic ganglion is noted as its branches make a connection with the branches of the first mesothoracic nerve. Wherever possible an attempt has been made to relate the observations to those of some other authors.

SUMMARYThe leaf hairs (trichomes) on the aerial surface of many plant species play important roles in phytochemical production and herbivore protection, and have significant applications in the chemical and agricultural industries. Trichome formation in the model plant Arabidopsis thaliana also presents a tractable experimental system to study cell differentiation and pattern formation in plants and animals. Studies of this developmental process suggest that trichome positioning may be the result of a selfforming pattern, emerging from a lateral inhibition mechanism determined by a network of regulatory factors. Critical to the continued success of these studies is the ability to quantitatively characterize trichome pattern phenotypes in response to mutations in the genes that regulate this process. Advanced protocols for the observation of changes in trichome patterns can be expensive and/or time consuming, and lack user-friendly analysis tools. In order to address some of these challenges, we describe here a strategy based on polarized light microscopy for the quick and accurate measurement of trichome positions, and provide an online tool designed for the quantitative analyses of trichome number, density and patterning.