422 CRUSTACEA ENTOMOSTEACA. 



long tail ending in two filaments. "Giant spermatozoa" have 

 been observed, though rarely, in Balanus perforatus, by Gruvel. 



The ovaries as already stated lie as a single mass in the peduncle 

 of the Lepadidae, and in the corresponding basal region of the 

 body in the Operculata. The paired oviducts open, not near 

 the base of the abdomen, as usual in the Crustacea, but on pro- 

 minences on the basal joints of the anterior pair of thoracic 

 appendages. The eggs undergo their development in the 

 mantle space, contained in two flattened gelatinous sacs, com- 

 parable to the ovisacs of the Copepods, which lie one on each 

 side and are attached (in the Lepadidae) to the ovigerous frena. 

 The mode of fertilization is described by Gruvel. In Lepas two 

 individuals of a cluster come together, one of them, assuming 

 the part of the male, deposits a viscous mass of spermatozoa 

 on either side of the mantle cavity of the other, in the region 

 of the orifice of the oviduct. The penis of a large individual 

 may attain a length of 4-5 centimetres. A similar process 

 has been observed in Balanus. Gruvel has observed self-fertiliza- 

 tion to occur in an isolated specimen of Pollicipes. 



The species of the genera Ibla and Scalpellum offer remarkable 

 instances of sexual relationship. Most if not all are dimorphic ; 

 The species consists in some cases of hermaphrodite forms 

 resembling those of allied genera of Lepadidae, but with certain 

 dwarf male forms in addition, the " eomplemental males." 

 In other cases the two forms constituting the species are male 

 and female the latter resembling the hermaphrodite forms of 

 their allies, though without the male generative organs. In 

 all, the male forms are small and are attached either in a pouch 

 within the scutum or elsewhere about the mantle of the other 

 form. They exhibit various degrees of arrested development 

 and degeneration. Further details are given below. 



The Acrothoracica are also dioecious, the males being degener- 

 ate and much reduced in size. 



The Cirripedia are marine animals and attach themselves to 

 various foreign objects. They are found fixed, usually in groups, 

 to logs of wood, rocks, mussel shells, Crustacea, the skin of 

 whales, Hydrozoan colonies, etc. Some as Lithotrya, Alcippe 

 and the Acrothoracica, are able to bore into the shells of Molluscs 

 and Corals. 



The members of the sub-orders Apoda, Rhizocephala and 



