2. The moulting of the mantle-cavity and of the vas deferens and the passage of the ova into the mantle-cavity. 25 



always in Sacculina the external chitinous investment and the lining of the mantle-cavity and 

 vasa deferentia are cast off separately, a rupture taking place at the mantle-opening. 



The moulting of the mantle-cavity and of the vasa deferentia always occurs soon after 

 the nauplii in the mantle-cavity have been set free, and immediately before the new brood 

 of eggs is passed into the mantle-cavity for fertilization. The interval between the emission 

 of the nauplii of one brood and the deposition of the eggs of the next brood varies in length 

 according to the species, and also according to the physiological condition of the individuai. 

 Delage observed this interval in Sacculina carcini to be about four days, while I have found it 

 in Sacculina neglecta to be usually less than twenty-four hours. In Peltogaster curvatus four or 

 six days usually elapse before the mantle-cavity moults and receives its new brood of eggs. 



The moulting of the mantle-cavity between the emission of the nauplii of one brood 

 and the passage of the eggs of the next brood from the ovary into the mantle-cavity, serves 

 two purposes: in the first place it cleanses the mantle-cavity of the débris left from the last 

 brood of embryos, and secondly it removes the chitinous plug from the vasa deferentia which 

 would otherwise block the way for the entrance of the spermatozoa into the mantle-cavity. 

 The effectual method in which the vas deferens may be blocked by this chitinous plug is 

 shown in Piate 2 fig. 13 which represents a section through the opening of the vas deferens in 

 Parthenopea. 



In Sacculina, moreover, the moult serves another purpose, for in this forni special chitinous 

 hooks or retinacula are present on the internai surface of the mantle-cavity for holding the 

 egg-tubes fast, and the moulting of the mantle-cavity after the liberation of one brood of 

 nauplii is necessary to expose the new chitinous lining with its fresh set of retinacula on it. 



The foregoing account applies to the preparations for the fertilization of ali the batches 

 of eggs except the first. 



But previously to the entrance of the first batch of eggs into the mantle-cavity the 

 latter has been empty, and as a matter of fact no moult takes place immediately before the 

 passage of the eggs. But the necessity for this is obviated by the fact that during the early 

 stages in growth preceding the maturation of the first brood of eggs, the chitin lining the 

 internai surface of the mantle and of the vasa deferentia never attains to sufficient thickness 

 to occlude the openings of the vasa deferentia into the mantle-cavity. 1 have proved on 

 numerous occasions in Sacculina neglecta that at, and immediately after, the moment when the 

 first brood of eggs is passed into the mantle-cavity, the chitinous lining of the mantle-cavity and 

 of the vasa deferentia was exceedingly thin, and left a free passage for the spermatozoa to reach 

 the eggs in the mantle-cavity, a passage which they had evidently availed themselves of, as 

 the testes were devoid of spermatozoa, which were found lying among the eggs in the 

 mantle-cavity. 



It is therefore equally possible for self-fertilization to occur in the first brood of eggs 

 as in the succeeding broods, and in fact it always does occur. 



Zool. Station zu Neapel, Flora iind Fauna, Golf von Neapel. EMzoeephala. 4 



