- Yellowthroat
- Yellow-shafted Flicker
- Yellow-headed Blackbird
- Yellow-breasted Chat
- Yellow-billed Cuckoo
- Yellow Warbler
- Wood Thrush
- Wilson’s Warbler
- Wilson’s Snipe
- Wilson’s Phalarope
- White-crowned Sparrow
- White-breasted Nuthatch
- White Pelican
- Warbling Vireo
- Vesper Sparrow
- Various species of Trypanosoma from the blood of mammals, birds, and reptiles
- Upland Plover
- Turkey Vulture
- Tufted Titmouse
- Trypanosoma Ziemanni, from the gut of the gnat
- Trypanosoma Ziemanni, from the blood of the little owl
- Tree Swallow
- The ‘Wonderful Cynocephalus’
- The young of the common Eel and its metamorphosis
- The unicellular parasite Benedenia, from the gut of the common Poulp or Octopus
- The short strap in use
- The short and the long straps
- The Number of the Chromosomes
- The Horse lying down
- The Freshwater Jelly-fish of Regent’s Park (Limnocodium Sowerbii)
- The Freshwater Jelly-fish of Lake Tanganyika
- The earliest discovered Trypanosome, described by Gruby in 1843
- The Ash-Coloured Buzzard
- The application of both straps
- Teaching the horse to back
- Summer Tanager
- Starling
- Spotted Sandpiper
- Sparrow Hawk
- Song Sparrow
- Snowy Egret
- Snow Goose
- Slate-colored Junco
- Screech Owl
- Scotch Colley, or Shepherds Dog
- Ruddy Duck
- Ruby-throated Hummingbird
- Ruby-crowned Kinglet
- Robin
- Ring-billed Gull
- Remorse from an elephant
- Red-winged Blackbird
- Red-tailed Hawk
- Red-headed Woodpecker
- Red-eyed Vireo
- Red-eyed Towhee
- Red-bellied Woodpecker
- Purple Martin
- Preparing to lie down
- Prairie Chicken