THE REPRODUCTIVE SYSTEM OF E. SUPERBA 347 



of the parts may be sufficient to bring about transfer, but that the musculature alone 

 cannot be effective. It is difficult to understand why he made this statement. The 

 muscular system in E. superba is well developed, both in the body and in the appendages, 

 and there is no anatomical evidence to show that the animal is not capable of the 

 sustained muscular effort necessary to effect fertilization. The whole problem is one 

 which can only be solved by observation of living material, but examination of well- 

 preserved specimens confirms Zimmer's suggestions, in the main, as to the method of 

 the transference of the spermatophores. 



The spermatophores are held in the thelycum by a chitinous cement substance 

 adhering to their necks, and secreted by the lateral pockets of the spermatophore sacs 

 in sufficient quantity to plug the mouth of the thelycum. The spermatozoa spm (Fig. 25) 

 form a white mass in the wider end of the spermatophores when transference has just 

 taken place, but very soon they penetrate up the narrow necks into the cavity of the 

 thelycum itself, filling it completely and extending right up to the posterior opening, 

 next to the female genital pores egp (Fig. 25 and Plate V, fig. 3). This penetration is 

 effected by the action of a fluid contained in the spermatophores together with the 

 spermatozoa, and which is secreted by the cell lining of the vasa deferentia in the region 

 of the posterior flexure (see p. 334). This fluid expands, according to Raab, and pushes 

 the sperm mass spm before it out of the spermatophore. 



Koltzoff (1906) described a similar process in some Decapoda, the spermatophores 

 of which contain a fluid, which swells so prodigiously that it ruptures the chitinous 

 sheath, and shoots the sperm through the egg membrane, thus bringing about fertiliza- 

 tion. He called this substance "Explosionsstoff ". 



The passage of the spermatozoa into the cavity of the thelycum must be rapid, for it 

 is much more usual to find the spermatophores empty and the thelycum full than 

 vice versa, although specimens showing the latter condition occur sometimes in a big 

 catch. 



Copulation generally occurs when the eggs have only reached a quarter or a third of 

 their diameter when ripe. The spermatozoa must therefore retain their potency for 

 some time. Normally, two spermatophores are inserted into the thelycum, but any 

 number up to seven has been seen. In those specimens where copulation has occurred 

 more than once, the spermatophores often show all stages between empty and full, 

 indicating that they were affixed at successive intervals of time, and that possibly all of 

 the spermatozoa are unable to penetrate at once into the thelycum, as its capacity is 

 limited. 



As the eggs are laid, they come into contact with the sperm mass (Fig. 25 and Plate V, 

 fig. 3), and fertilization is effected. Andrews (1904), in a detailed account of the breeding 

 habits of the American crayfish, writes as follows: "As the eggs are laid they probably 

 pass over the annulus [cf. thelycum in Euphausid] and a relatively small amount of 

 sperm might fertilize all of them, if it came out of the sperm plug in time. Before laying 

 the annulus is covered with glair and possibly this may act to bring the sperms out, as 

 well as to protect them from the water. . . . Some osmotic factor may be here concerned 



