l-^ HOLMES. [VOL. II. 



but little wider than the body of its occupant, no one who 

 watches the operation can fail to have a feeling of admiration 

 for the neatness and extreme quickness of this acrobatic feat. 

 The animal executes this " about face" with such rapidity that 

 it is only after watching the operation repeatedly that one can 

 determine how it is effected. As the animal lies in its nest 

 the abdomen is bent forward and the posterior pairs of thoracic 

 legs are directed backward, their claws being usually hooked 

 into the walls of the nest. When about to turn around, the 

 abdomen is thrust forward, its terminal hooks caught in the nest ; 

 the tip of the abdomen, therefore, forms a fixed point, and the 

 insertion of the thoracic legs forms another. The contraction of 

 the legs would therefore pull the middle and anterior parts of the 

 body backward. When the head is pulled back some distance, 

 extension of the body occurs, forcing the anterior part of the 

 body through to the other end of the nest. The head end 

 being reversed, the abdomen is loosened and quickly flexed 

 again under the body. The whole operation is completed in 

 less than a second, and the animal may be made to repeat the 

 performance several times in rapid succession. 



Nests and Nest-Building. 



The nests of Amphithoe are tubular structures which gener- 

 ally exceed somewhat the length of the animal. They are 

 made of a web-like material which, under the microscope, may 

 be seen to be a network of exceedingly fine threads. The 

 nests are usually constructed among the branches of the red 

 seaweeds or upon the leaves of eel-grass or the fronds of Ulva. 

 When built upon Ulva the nest is generally located in a wrinkle 

 or fold of the surface which affords a partial shelter. The nest 

 is open at both ends and is of about the same diameter through- 

 out. Foreign materials, such as bits of seaweed, are usually 

 woven into the nest and greatly add to its efficiency as a means 

 of concealment. Amphithoe frequently leaves its nest, but I 

 could find no evidence that it would return to its own nest 

 more readily than to any other ; it will simply enter the first 

 unoccupied nest that comes in its way. When established in 



