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1. Properties of Botryllus schlosseri which give it outstanding promise for studies in developmental genetics are reviewed. 2. Laboratory culture procedures, in vitro fertilization, and a method for raising embryos in vitro are described. Controlled successions of complete life cycles can now be achieved in any laboratory. 3. Experiments involving colony fusion, subsequent vascular budding, and the analysis of color patterns in resultant systems suggest that cells of the simple vessel walls govern the morphology of the regenerated zooids. 4. Results of some preliminary genetic crosses are reported.

At each of five loci in 829 Escherichia coli clones from 156 samples from diverse natural sources, electrophoretic analysis reveals a prominent mobility class (frequency over 0.70) and 2 to 11 distinct mobility classes at lower frequencies. The frequency distribution of the classes argues against the importance of neutral mutations in allozymic variation. Heterosis is not the universal cause of genic polymorphism.

A DNA sequence in Eschenchia coil K-12 contais an evident gene, kch, which predicts a protein 417 residues long with extensive simii to a group of eukaryotic potassium channel proteins in amino acid sequence, in the presence ofsix apparent tmembrane (S) The molecular ancestry of eukaryotic voltage-gated cation channels is obscure, beyond the likelihood that a potassium channel came first. This likelihood is based on the similarity between potassium channel proteins and other cation channel proteins in a set of six transmembrane domains with a cation-specific pore located between the fifth and sixth domains. While potassium channel proteins contain no more than one such set of domains, sodium and calcium channel proteins contain four sets in linear order, implying a history of two duplication events (1). Here

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1. Ecdysone is in a highly dynamic state after its injection or its secretion by the ring-gland of Sarcophaga peregrina. Hormonal activity is rapidly destroyed by an inactivating mechanism which is present in the tissues but not in the blood. 2. Inactivation is blocked by low temperatures or anaerobic conditions-a finding that implicates chemical and, more particularly, oxidative reactions. The mechanism in question could be demonstrated in larval fragments but not in crude or fractionated homogenates. 3. When injected into mature larvae, 1 µg of α-ecdysone loses 50% of its activity in 1 hour and 98% in 8 hours. Lower doses show even briefer "half-lives." 4. The rapid inactivation of ecdysone can account for its low titer in both the blood and tissues. Thus at the "critical period" for puparium formation, the entire larva contains only 2.5 nanograms, corresponding to only 7% of a Sarcophaga unit. 5. The evidence points to the accumulation, not of the hormone itself, but the covert biochemical and biophysical effects of the hormone. The covert effects undergo spatial and temporal summation within the target organs and finally discharge the overt developmental response. 6. The role of the blood is to serve, not as a reservoir, but as a pipeline through which ecdysone flows from the ring-gland to its sites of action and swift inactivation.

Day old Drosophila pupae were subjected to a variety of closely controlled temperature shocks. Twenty-five hours after pupaxium formation (at 23°), temperatures from 39.5-41.5 ° (Q1 = 2.3) differentially disturb the formation of the posterior crossvein. Three other separate treatments disturb posterior crossvein formation: treatments in the range 36.0-37.0 ° at 25 hours; 37.3-37.8 ° at 25 hours; and 39.5-41.5 ° at 19 hours. Certain qualitative effects are associated with certain temperatures: elliptical holes are seen in wings of flies exposed 25 hours after puparium formation to temperatures from 37.3-37.8 °. Anterior crossvein defects ensue if animals axe similarly exposed to temperatures from 37.9-38.2 ° . Within the physiological range, animals raised at higher temperatures are more resistant to the effects of temperatures at 39.5-41.5 ° . An extremely rapid temperature adaptation by exposures to temperatures in the range 31-38 ° results in markedly greater resistance to heat shock; here resistance to production of crossvein defects increases faster than to death. The association between qualitative effects and treatment temperatures is modified by changing the temperature at which the animals spend their first day of pupal life. Summation experiments support conclusions drawn from the simpler experiments. Genetic variation and interspecific variation are discussed in the present context, as well as implications of the role of protein denaturation in the biological effects of high temperatures and further, more general experiments. I N T R O D U C T I O NT h e posterior crossvein of Drosophila melanogaster provides a good biological end point for the study of t e m p e r a t u r e effects. T h e structure is linear, a n d its d e v e l o p m e n t is m o r e labile at certain temperatures t h a n a n y other c o n t e m p oraneous observable developmental process. M o r e o v e r , study of this crossvein does not require its isolation, and so we can d r a w conclusions with some assurance as to the validity of measurements m a d e a n d their i m p o r t a n c e to the organism. In a study originally designed to lay the foundation for a sensitive analysis of genetic variation, a n u m b e r of r a t h e r r e m a r k a b l e p h e n o m e n a were observed. T h e investigation of various t e m p e r a t u r e effects o n d a y old

Nucleotide sequences of translated regions of the trp operon in 12 wild strains of Escherichia coli reveal striking uniformity among eight strains (suggesting recent common ancestry and supporting the importance of periodic selection in natural populations) and clustered substitutions in four strains (implicating events affecting runs of nucleotides).