GROWTH AND LIFE HISTORIES 71 



The details of egg attachment in the decapods vary from family 

 to family, but as a general rule the free-swimming Caridea do not 

 have eggs attached to the last pair of pleopods, and they retain the 

 ability to flex the abdomen. Sudden flexing of the abdomen, 

 producing a backward darting movement, is an important escape 

 movement. The retention of this ability by an egg-bearing female 

 is clearly of survival value to a species. 



Most of the Peracarida retain their eggs in a brood pouch formed 

 by plates, or oostegites, which project inwards from the bases of 

 one or more pairs of the walking legs. Some of the Tanaidae have 

 only one pair of oostegites, but up to seven pairs are found in some 

 of the Mvsidacea. Deviations from the normal peracaridan brood 

 pouch are found among certain isopods. Sphaeroma retains the eggs 

 in pouches which project into the body from the ventral surface. 



A unique brood pouch is found in the Thermosbaenacea. These 

 are the only Malacostraca which carrv their eggs on their backs, 

 in a pouch formed by the carapace. The female lies on her back 

 when she lays her eggs, and they drop into the pouch. 



A dorsal brood pouch, between the body and the carapace, is 

 also found in the Cladocera and Conchostraca: in the latter group 

 there are special processes from some of the limbs which help to 

 keep the eggs in place. The brood pouches of some Cladocera, such 

 as Moina, are closed, and there appears to be a nutritive secretion 

 passed into the pouch by the mother. The eggs of Moina cannot 

 develop if removed from the brood pouch, whereas the Cladocera 

 with open brood pouches (Daphnia, Chydorus, etc.) produce eggs 

 which will develop outside the brood pouch, even in distilled water. 



Some ostracods also carry their eggs between the body and the 

 carapace, sometimes until hatching, but more usually the eggs are 

 deposited freely in the water, or are attached to plants and stones. 

 In the cirripedes the eggs are retained until hatching in the mantle 

 cavity. 



Different locations of the brood pouch are found in the Notos- 

 traca and Anostraca. In the Notostraca there is a pouch on the 

 eleventh pair of legs; eggs are laid into this pouch at the beginning 

 of an instar and carried until the animal is ready to moult again. 

 The eggs are then extruded from the pouch and coated with a 

 sticky layer, hv means of which they are attached to grass roots 

 and similar objects. The Anostraca carry their eggs in a pouch 

 under the front part of the abdomen. In most species the eggs are 

 carried for an instar and then liberated, still only partly developed 



