Google is experimenting a new search interface that hides the sidebar options in a drop down menu by default. To access the sidebar's contents, you will have to click a small arrow icon to see the list of specialized search engines and some advanced search options that let you filter results.
"It can be seen that after performing a search at the top behind 'Everything' or Dutch 'All' a small arrow is placed. After clicking on it will come over all the options as shown in the image."
"The disadvantage is that immediately after clicking on another search engine such as Pictures menu is hidden again and so must be clicked open again if you want to use the options," posted Websonic, who also shared a video showing the new drop down in action.
Here is the image of the new drop down: