Robert W. Mead’s research while affiliated with University of Nevada, Reno and other places

Regeneration was examined in different regions of planaria (Dugesia tigrina) in order to determine the effect that the shape of a section exerts on proportion regulation during regeneration. Length: width ratios were used as an index of section shape and experiments utilized sections at which this ratio was below 1.0 Proportion regulation was evaluated by determining relative area of major body regions for normal and abnormal regenerates. Proportional area of body regions anterior to the pharynx increased with proportional decreases in the length: width ratio for all regenerates, but this increase was greater for regenerates that originated from segments anterior to the pharynx. Changes in proportional area of one anterior body region were closely correlated to changes in porportional area of other anterior body regions. The exact nature of these correlations varied as a function of originating segment. A hierarchy also exists in proportional head tissue between normal and abnormal regenerates as total relative head area of twoheaded regenerates was around three times that of normal planarians while regenerates with one large head and without a pharynx had a proportional head size that was less than that of two-headed animals but more than twice that of normal planarians.

The time interval between cuts that are made to obtain a tissue fragment from a planarian was found to be important to the process of its regeneration. Short fragments made by two transverse cuts across the body were more likely to regenerate abnormally when the interval between the two cuts was 5 or 12 min than when it was 1.5 min. The longer intervals specifically altered the regression line in the correlation between the length:width ratio of fragments and frequency of abnormal regenerates. This effect occured regardless of which region of the body the fragment was taken from. The time interval also affected body proportioning in regenerates and to the greatest degree in fragments derived from the region located immediately behind the head. These results indicate that events occuring shortly after a cut is made in a planarian significantly affect structure patterning and proportioning of the regenerate.

Epithelium of the sea anemone Acontiophorum niveum is modified into four general arrangements of microappendages: (1) uniform microvilli covering pedal disc and column, (2) an interspersion of microvilli, ciliary cones, and kinocilia on tentacles, (3) flagella among an understory of microvilli from the oral disc, actinopharynx, filaments, and acontia, and (4) sparse flagella among irregular microvilli from endoderm. These arrangements are similar to those described previously in the epithelia of other anthozoans.

1.1. Injection of [U-14C]aspartic acid into juvenile Macrobrachium rosenbergii resulted in no label being incorporated into asparagine.2.2. Labelled taurine was observed 24 hr post injection of [U-14C]serine. Radioactivity was also detected in glycine.3.3. The turnover rate of injected [U-14C]taurine suggests a half-life of greater than 28 days in the prawn.4.4. Results suggest that a dietary requirement for asparagine may exist in the prawn. In addition, the prawn's nutritional requirement of taurine may be fulfilled by its biosynthesis.

1.1. Taurine concentrations were determined in various organs dissected from juvenile Macrobrachium rosenbergii.2.2. Heart and nervous tissue had the highest taurine concentrations; this suggests that taurine may function in cardiac and neural processes in the prawn.3.3. Relative free amino acid concentrations were determined to investigate changes in concentration following acclimation to various salinities.4.4. No significant change in taurine concentration in the prawns was demonstrated at any salinity tested. However, the concentration of alanine increased significantly between 15–20%. The elevated alanine concentration suggests it may function in osmoregulation.

Stem cell frequency, wet weight, proglottid number, and egg production were measured in Hymenolepis citelli at specific intervals between 20 and 120 days postinfection in an effort to correlate changes in stem cell frequency to other developmental parameters. Considerable variability was seen in wet weight and proglottid number, but differences did not seem to reflect any relation between these parameters and stem cell frequency. Significant differences were observed in egg production at specific postinfection periods. These appeared to correspond to changes seen in stem cell frequency during patency. Similar changes in egg production which also correspond to measured changes in stem cell frequency were recorded for Hymenolepis diminuta. Differences were also seen in number of eggs contained within gravid proglottids at various times postinfection for both species.

Regeneration was examined in different regions of planaria (Dugesia tigrina) in order to determine the effect that the shape of a section exerts on regenerative success. Length:width ratios were used as an index of tissue proportion, and overall regenerative success was measured by percent of abnormal regenerates and number of abnormalities per abnormal regenerate. Frequency and number of abnormalities increased as section width exceeded section length. Frequency of specific abnormalities varied with changes in length:width ratios and followed a predictable pattern. As ratios decreased below 1.0, abnormalities typically consisted of characteristics regarded as being due to excess head formation. These included the presence of two heads, the “head hump” syndrome, and/or lack of pharynx. This excess head formation was due to the proportional shape of the section rather than to overall segment size, and the frequency of such abnormalities increased in proportion to decreases in length:width ratios. Abnormalities which were more typically seen at ratios over 1.0 consisted of the lack of head, pharynx, and/or polarity.

Regeneration was examined in fissioned and unfissioned planarians (Dugesia tigrina) in terms of regenerative success and body proportioning. Regenerative success was determined in terms of percent of abnormal regenerates and number of abnormalities per abnormal regenerate. Sections from unfissioned animals were less successful at regeneration than were those from fissioned animals, and body regions located immediately behind the pharynx represented those segments which formed fewer abnormal regenerates as a result of fissioning. Body proportioning was measured as a function of size of head and prepharygeal region to overall body length. A direct correlation was seen in the proportional size of these two parameters, which varied significantly among regenerates. Results suggest that body proportioning is not constant from one excised piece to another but is predictable and dependent on several variables including interval between fission and sectioning, region from which the segment was obtained, and/or original length of the segment.