These little monsters are German Hunt Terriers or Jagd Terriers. Back in 2004, I wrote the first true history of the breed which I was able to cobble together based on a guess that Lutz Heck would likely have been involved. He was, as I discovered by diving into the stacks at Harvard and Yale. Not everyone is happy with my history of this breed, or my description, but the former is true and the latter is accurate.
For those interested in Lutz Heck, he was also instrumental in creating the modern Auroch look-alike (Nazi-bred Super Cattle in the U.K.), as well as the Quagga and the Tarpan.
For those interested in how myths about wildlife and pet and farm animals got wrapped up in national identity in the first half of the 20th Century, this post on "A Cuckoo In the House of James Bond's 'M'" might be of interest.