Google sheets: possible to increment row references rather than column references using fill-down?

When using fill down on a column is it possible to increment row references rather than column references:

| --------------------- |  
| =dogs!B15+cats!B27    |  
| --------------------- |  
| =dogs!C15+cats!C27    |  
| --------------------- |  
| =dogs!D15+cats!D27    |  
| --------------------- |  

rather than:

| --------------------- |  
| =dogs!B15+cats!B27    |  
| --------------------- |  
| =dogs!B16+cats!B28    |  
| --------------------- |  
| =dogs!B17+cats!B29    |  
| --------------------- |