348 DISCOVERY REPORTS 



in bringing out the sperm. Other means of getting the sperm out of the waxy tube, that 

 we have called the sperm plug, and from the interior of the annulus might be the 

 pressure that the sternal plate between the fifth legs may exert on the annulus when the 

 legs are forced forwards, as seemed to be the case about the time of laying." 



In E. superba, it seems likely that owing to the close proximity of the genital pores 

 to the free end of the sperm mass (Fig. 25), the pressure due to the extrusion of the eggs 

 will be sufficient to liberate the sperms at the same time from the posterior opening of 

 the thelycum, and thus bring about fertilization. The shell membrane is probably still 

 soft and glutinous, and will therefore allow the passage of the sperms through it. 



Meyer (1934) found that in Crangon vulgaris the shell membrane remained soft for 

 some time after laying, the hardening process being a gradual one. 



In spite of the large number of eggs ( 1 1 ,230 and 1 1 ,407 were counted from the ovaries 

 of two gravid females respectively), the process of laying is evidently a rapid one. On 

 two occasions, females with greatly distended carapaces and carrying spermatophores 

 were placed for observation in the aquarium on board the R.R.S. 'Discovery II'; 

 these spawned overnight, and the following morning eggs were found in the water. 

 One of the females was dissected and "many eggs were found in the ovary, floating 

 in a milky fluid, which appeared to consist of an emulsion of tiny oil globules. The 

 eggs were the same size as those found in the aquarium", that is o-6 mm. in diameter. 

 Spawning in this instance was clearly incomplete, and this was probably due to the 

 fact that, normally, gravid females occur at depths of 250 m. and more, where perhaps 

 the increased pressure of the water assists in the liberation of the eggs. The eggs failed 

 to develop in the aquarium, because the external conditions were not suitable. 



After the eggs have been laid, the ovary resumes its primitive saddle shape, and the 

 shell glands are still much in evidence, extending up the oviduct for some distance, 

 as well as remaining in the coxopodites of the legs. 



SUMMARY 



1. Dissection shows that both male and female reproductive systems are developed 

 before any external sexual characters appear. The sex of each specimen can be deter- 

 mined in this way. 



2. A series of stages in the development of the male and female systems was obtained. 



3. Modification of the first pair of pleopods begins before the second pair shows any 

 sign of diff^erentiation. 



4. The course of the oviducts through the shell glands was traced by means of serial 

 sections as well as by dissection. 



5. Transference of spermatophores occurs in the first place before the female is 

 gravid. 



6. The spermatozoa retain their potency for some time. 



7. Fertilization is external, occurring when the eggs are laid. 



8. Spawning takes place rapidly, probably at depths of 200 m. and below. 



