Table 1.

Comparison of the evolution history of diapedesis mechanisms by interacting components.

Species	Brain Structure	Immune Cells	BBB	Critical Component		Known Diapedesis Mechanism
				Cav1	Pecam1
T. adhaerens	No brain detected	No known immune cells	No	Yes	no	NA
N. vectensis	Two brain pathways observed	Ameboyctes	unknown	Yes	no	NA
C. elegans	Brain-like structure	No adaptive immune system or mobile immune cells identified	glia	Yes	No	NA
D. melanogaster	Brain-like structure	Hemocytes	septal	no	no	Likely Paracellular
C. intestinalis	177 neurons identified	Hemocytes	unknown	Yes	No	Likely transcellular
P. marinus	Brian structure exits	VLAR, VLARB and VLARC cells	Yes	Yes	No	Likely transcellular
Marine vertebrates	Brian structure exists	Adaptive and innate system developed	yes	Yes	Yes	Transcellular and paracellular
Terrestrial vertebrates	Brian structure exists	Adaptive and innate system developed	yes	Yes	Yes	Transcellular and paracellular