484 



CRUSTACEA MALACOSTRACA. 



a. 



segment but one, into the brood cavity. A new batch of eggs is fertilized 

 later in the ovary by sperm left over from the first copulation, and this 

 reaches the brood cavity in the same way. After this second batch of 

 eggs has been developed in the brood cavity and the young that are 

 hatched have left it, the animal moults, and then again appears as it was 

 before copulation. (Lang.) 



In Sphaeroma rugicauda the greater part of the development 

 of the young occurs, not in the brood space but in four paired 



brood sacks, formed by in- 

 vagination of the ventral 

 wall of the thorax and ly- 

 ing within the body. The 

 young must enter these 

 sacks soon after the eggs are 

 hatched.* 



Among the Cymothb'ina 

 which are parasitic in the 

 mouth and branchial 

 cavities of fishes, three 

 genera (Cymothoa, Anilocra 

 and Nerocila) have been 

 found to be hermaphrodite, "f" 

 being male when young and 

 acquiring female characters 

 at a later period. 



In the young stage they 

 possess three pairs of testes, 

 two rudimentary ovaries 

 internal to the testes, a 

 paired copulatory organ into which the two vasa def erentia open 

 (Fig. 298), and the stylif orm processes of the male on the second 

 abdominal legs. In the course of further growth, including two 

 moults, the testes diminish and the external male organs dis- 

 appear, while the ovaries develop and oostegites grow out 

 from the ventral surface. Henceforward the animal is female. 

 Many Epicaridea are similarly hermaphrodite ; they are referred 

 to below in relation with the metamorphosis of Isopods. 

 The embryonic development begins after the entry of the eggs 



* Leichmann. Bibl. Zool. Hft. 10. 



f J. Bullar, The generative organs of the Parasitic Isopoda, Journ. 

 Anat. Physiol., 1876. P. Mayer, Ueber den Hermaphroditismus einiger 

 Tsopoden, Mittheil. aus der Zool. Stat. Neapel, 1879. 



FIG. 298. a Female phase of Cymothoa 

 Banksi (after M. Edwards). Bpr oostegite. 

 b sexual organs from a young Cymothoa 

 fiestrides (after P. Mayer). Od oviduct ; 

 Ov ovary ; P penis ; T the three testes ; 

 Vd vas deferens (from Claus). 



