| They also lack arrector pili, so their fur can be streamlined as they swim. |
| In fact, the arrector pili muscle and the sebaceous glands are missing. |
| At the hair follicle, one or several sebaceous glands and an arrector pili muscle, which causes the hair to stand on end, can be found. |
| Associated with the follicle are sebaceous glands and the arrector pili smooth muscle fiber bundle. |
| The glands discharge their contents by the contraction of the arrector pili muscle and by any pressure applied to the gland. |
| When these structures were placed into the recipient area, the hair unit, including arrector pili muscle and neural connections, also developed. |
