The timing of the first meiotic cycle in the young male mouse was established by serial sacrifices and subsequent paraffin sectioning of testis and epididymis. Meiosis commences in mice 8 to 10 days old. The highest frequency of any one phase of meiosis was found at days 17 to 19, when 47 percent of the tubules were found to contain late pachytene.

We compared the hematologic parameters of 18 otherwise healthy children with Down syndrome (DS) in the age range of 2-6 years to those of 18 healthy non-DS controls matched for age and gender. The children with DS had MCVs and hematocrits increased significantly compared to controls and decreased WBCs compared to controls; 66% of the children with DS compared to 11% of non-DS controls had MCVs greater than the 97th percentile for age (P < 0.0001); the mean MCVs were 86.9 and 80.6, respectively. Although hematocrits were within normal limits for age for all DS and non-DS subjects, the DS patients had significantly higher hematocrits (39.1% vs. 36.9%, P < 0.014). We also found that 33% of the children had WBCs < 5% for age compared to 6% of controls. To determine whether folate deficiency contributed to these observations, we measured serum and RBC folate concentrations: these were not significantly different between the 2 groups. We conclude that macrocytosis and leukopenia are common in children with DS.

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