Estimates of the number of different cell types in the human body remain uncertain, with varying opinions on the classification of neurons ranging from a single cell type to each neuron being unique. Identifying cell types typically relies on distinguishing characteristics such as cell morphology and function, with molecular components providing additional criteria for analysis. Recent advancements in technology have revolutionized cell type analysis, particularly through mRNA sequencing in small organisms like flatworms, roundworms, zebrafish, and frog embryos. These methods enable researchers to group and analyze transcripts from the same cell, highlighting that distinct cell types express different sets of genes, as reflected in their RNA. Furthermore, these techniques allow for tracking the developmental pathways of cell types over time. However, access to this research is limited, with much of it not available in open access formats.