What is In megaloblastic anemia, the cells are: and explain in detail?
Megaloblastic Anemia 
The blood film can point towards vitamin deficiency:

Decreased red blood cell (RBC) count and hemoglobin levels.
Increased mean corpuscular volume (MCV >100 fL) and mean corpuscular hemoglobin (MCH).
Normal mean corpuscular hemoglobin concentration (MCHM = 32-36 g/dL). 
Decreased reticulocyte count due to destruction of fragile and abnormal megaloblastic erythroid precursor. 
The platelet count may be reduced.
Neutrophil granulocytes may show multisegmented nuclei ("senile neutrophil”). This is thought to be due to decreased production and a compensatory prolonged lifespan for circulating neutrophils, which increase the numbers of nuclear segments with age.
Anisocytosis (increased variation in RBC size) and poikilocytosis (abnormally shaped RBCs).
Macrocytes (larger than normal RBCs) are present.
Ovalocytes (oval-shaped RBCs) are present.
Howell-Jolly bodies (chromosomal remnant) also present.