98 BALANIDJE. 



stag's horns, with the extremities a little enlarged : a figure* 

 of a small portion from Balanus perforatus is given in 

 PI. 25, fig. 2. It is quite surprising how like in struc- 

 ture and appearance the branching ovarian tubes often are 

 to the testes with their ducts; but the latter are of smaller 

 diameter. Two main ducts generally unite just before 

 entering the broad, often reflexed, end of the vesicula 

 seminalis : in Coronula balcenaris, however, I observed four 

 ducts entering this receptacle. The two vesiculae seminales, 

 lying within the thorax and prosoma, are usually very long 

 and tortuous : they are formed of a thin inner tunic, which 

 is strengthened by thicker reticulated lines, and of an outer 

 layer of transverse fibres, which are either elastic, or probably 

 muscular, as they serve to expel the contents with force when 

 the end is cut off. The inner tunic is prolonged up the 

 probosciformed penis, at the base of which the two vesiculae 

 unite. f The contents of the vesiculae are commonly pulpy 

 and cellular; and from the cells the spermatozoa are de- 

 veloped ; soon after their development, they are, as it ap- 

 pears, expelled. 



I have seen the spermatozoa in Balanus crenatus, 

 perforatus, and balanoides, and in Chthamalus stellatus. 

 The cells, from which the spermatozoa are developed, and 

 which are often found in vast numbers within the vesiculae, 

 are on an average about ^th of an inch in diameter. The 

 spermatozoa differ remarkably within the vesicula of the 

 same individual, according to their state of development. I 

 have observed in B. perforatus and in the Chthamalus, that 

 the shortest, and therefore, I presume, the youngest (PL 29, 

 fig. 7, a), had a globular head with no projection in front : as 

 they increased in size, this head became less in diameter, 

 and a short tapering filament, {a, b y ) like the tail, projected 

 out of it. This anterior filament does not lie in exactly the 

 same line with the posterior filament, which is straight as an 

 arrow. In Bal. crenatus, the anterior filament was ^th of 

 an inch in length, and the posterior filament ^th, giving a 



* A far better figure is given by Karsten (' Nov. Act. Acad. Cses. Nat. 

 Cur.' 1S45, PL 20, figs. 2, 3, 4), but under the erroneous supposition that 

 these organs were hepatic. 



f In Conchoderma auri/a, the ducts, as shown by Burmcister ('Beitrage,' &c. 

 tab. ii, fig. 17), unite half way up the probosciformed penis. 



