OVIPOSITION, CARE OF THE BROOD. 105 



eggs are crowded together in a brood-cavity {e.g., in the Arthro- 

 straca), their shape, during the first stages of development, may be 

 rather irregular, on account of mutual pressure. 



It has been observed that, in various Crustacea, the female under- 

 goes ecdysis before laying the eggs. This is the case with some 

 Cladocera before the laying of the summer eggs (Jurine, Grobben), 

 also with Gammarus (Della Vallb) and Alyephyra (Ischikawa). 



The adaptations for the protection of the eggs vary greatly. The 

 eggs are laid singly {Cypris among the Ostracoda and Cetochilus, 

 Dias, Centropages among the Copepoda), or in bands (Arguhis), or 

 united into masses (Stomatopoda). The winter eggs of many of 

 the Cladocera are either, when laid, enclosed merely in their own 

 envelopes, or are further protected by a cuticular, saddle -shaped 

 structure, the so-called ephippium, which is a cuticular thickening 

 of the dorsal integument of the brood-chamber of the mother. The 

 summer eggs of this sub-order, on the contrary, undergo their entire 

 development within a brood-cavity, covered by the shell of the 

 mother, and a similar cavity shelters the eggs of the Notodelphyidae 

 (Copepoda) whilst they undergo development. In the Branchiopoda 

 there are many difterent adaptations for the protection of the eggs, 

 which are carried about by the mother until they reach a certain 

 stage of development. In Ajms, for example, the eggs are carried 

 in a watch-glass-shaped receptacle formed by processes of the eleventh 

 pair of limbs ; in Branchipus, in a pocket-like cavity of the abdomen ; 

 in Estheria, they are attached to filamentous appendages of the ninth 

 and tenth pairs of legs, situated between the valves of the mother's 

 shell. They are only deposited in the mud after the formation of 

 the blastoderm is completed and the outer germ-layer has developed. 

 Whereas, in the Ostracoda, the eggs are, as a rule, laid singly 

 (Cypridae), in Cypridina, they are retained within the shell of the 

 mother until they are hatched ; this is also the case in the Lepto- 

 straca {Nehalia) and in the Cirripedia. In the latter, the eggs are 

 cemented together in lamellae {Lepadldae) or enclosed in branched 

 ovisacs {Rhizocephala). In the Copepoda, except in the cases just 

 mentioned {Cetochihcs, Notodelphyldae), the eggs are carried in 

 ovisacs formed by a secretion of a special cement-gland, and are 

 attached to the genital segment. In the Arthrostraca, Cumacea, 

 and Mysidae, the eggs lie in a brood-chamber on the ventral side of 

 the thorax, externally protected by lamellate appendages (oostegites) 

 of the coxal joints of the thoracic limbs belonging to this region. 

 In the Decapoda, on the contrary, the eggs are usually attached 



