No earlier letters from Harris have been found. Harris has not been identified. Poplar is a district in East London. Admission to the Zoological Gardens of the Zoological Society of London on Sundays was restricted to fellows and their guests; by mid-century, paid public admission was available on other days. As a fellow of the Zoological Society, CD was entitled to sign an order of admission to allow guests admission, but these were not valid on Sunday, when only fellows were admitted; in practice, however, the regulations were often ignored and guests would be admitted with an order, without an accompanying fellow. For more on admission policies of the zoo and debates about Sunday admission, see Ito 2014, pp. 81–106.