70 A BIOLOGY OF CRUSTACEA 



in the Macrura and the dromiid crabs. r I'he second occurs in the 

 Anomura, while the third is found in the Brachyura other than the 

 dromiids. Some intermediate types are produced; the anomuran 

 Hippa pacifia makes a spermatophore which consists of a long 

 continuous tube which is attached along its length by means of a 

 ribbon-like stalk to a continuous strip. The macruran Parribacus 

 antarcticus produces a continuous tube which becomes twisted so 

 that pockets of sperms are formed, and on further twisting are 

 raised on coiled stalks. The brachyuran spermatophore is not left 

 on the outside of the female, but is passed into a special pocket, the 

 spermatheca, which lies internally at the base of the female duct. 



The transfer of the various types of spermatophore, or of free 

 sperms, to the female has the objective of ensuring that the eggs 

 are fertilised. Once fertilisation has taken place the care and atten- 

 tion given to the eggs is variable. 



Some Crustacea lay their eggs freely in the water. Certain 

 copepods, such as Calanus, some Bathynellacea, Anaspidacea, most 

 Euphausiacea and the penaeid prawns have this habit. Some 

 euphausiids and Neb alia carry their eggs between the thoracic 

 limbs, retaining them by means of the setae at the tips of these 

 limbs. The majority of decapods carry their eggs attached to their 

 abdominal appendages, and sometimes, as in Crangon, to the last 

 two thoracic limbs. The eggs are attached to special ovigerous setae 

 which have a cement secreted through them. This cement flows 

 over the eggs and binds them to the setae. In some species, such as 

 Leander squilla, the ovigerous setae are temporary structures which 

 only appear during the breeding season. The appearance of these 

 setae is probably controlled by hormones produced by the ovary. 

 If Leander is castrated, either by infection with the parasitic isopod 

 Bopyrus (see p. 1 15), or by exposure to X-rays, the ovigerous setae 

 are not formed. 



Fig. 32. Sexual dimorphism in the heads of Daphnia magna. 

 A, male. B, female. 



