EMBRYONIC AND LARVAL HISTORIES 63 



egg membranes and not as a free-swimming larval 

 form. But in a few of the Malacostraca, viz. in 



d.s 



A B 



Fig. 12. A. The mid-gut of Inachus mauritanicus with a young 

 Sacculina overlying it, x 2. c.t. "central tumour" of the para- 

 site; d.i., d.s., inferior and superior diverticula of alimentary 

 canal of host; n. "nucleus," or body-rudiment of Sacculina*, 

 r. its roots; x. definite position of the parasite. B. Later stage 

 in the development of the " Sacculina interna," x 2. b. body of 

 Sacculina', c.t. "central tumour " ; d.i., d.s., inferior and superior 

 diverticula of alimentary canal of host ; o. opening of perivisceral 

 cavity of Sacculina ; r. its roots. 



certain prawns, the animal hatches as a Nauplius, 

 agreeing in all essential details of structure with the 



