$2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I31 



function, degenerate and the ovaries begin to develop, so that the 

 former male larva thus changes functionally to a female. 



As a female, the parasite begins to increase in size. First the 

 proboscis elongates (fig. 19 E) and, though it is armed with only a 

 pair of minute teeth, it penetrates the integument of the crab. Inside 

 the host the proboscis stretches out to a long neck (F, Prb) until the 

 mouth {Mth) at the end comes in contact with the roots of the 

 Sacculina, and four diverging processes grow out around the mouth 

 to anchor the proboscis in the tissues of the crab. The body of the 

 newly feminized individual then takes on a saclike form (G). The 

 ovaries {Ov) are now fully developed; the oviducts open on two 

 pairs of ventral papillae. At this stage the female is inseminated by 

 a cryptoniscus larva still in the male phase of development (C). The 

 fertilized eggs are discharged into a large incubation chamber be- 

 neath the cuticle of the female. The process of forming the chamber 

 is somewhat complex as described by Caullery, but essentially it ap- 

 pears that two lateral ingrowths of the ventral ectoderm extend 

 inward around the sides of the body, and eventually close over the 

 orifices of the oviducts. When the eggs are discharged into the incu- 

 bation chamber, the female ceases to feed, doubles on herself in the 

 form of a U (H) and becomes a mere inert sac in which the eggs 

 complete their development. 



EUPHAUSIACEA 



The Euphausiacea and some of the Penaeidae are exceptional 

 among the Malacostraca in that they are hatched as nauplii. They are 

 both marine and entirely pelagic. The euphausiids go through many 

 moults before reaching the adult stage. Students of the group com- 

 monly distinguish five immature stages in the life history of an indi- 

 vidual. The first two are the nauplius and the metanauplius, the fol- 

 lowing three stages are termed the calyptopis, the furcillia, and the 

 cyrtopia. These forms, however, are merely stages of growth charac- 

 terized by different degrees of differentiation toward the adult struc- 

 ture (fig. 20 A-G). Except for the successive specialization of differ- 

 ent groups of appendages for swimming there are few metamorphic 

 changes involved in the development. The following condensed ac- 

 count of the typical life history of a euphausiid species is based on 

 the papers by Heegaard (1948) and Lebour (1925), with illustrations 

 taken from both. The order includes only a single family, the 

 Euphausiidae. 



The newly hatched euphausiid larva (fig. 20 A) is a typical nauplius 

 of simple form with the usual three pairs of appendages, a simple 



