[46] In _Conchoderma aurita_, the ducts, as shown by Burmeister ('Beiträge,' &c. tab. ii, fig. 17), unite half way up the probosciformed penis. 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 vesiculæ, are on an average about 1/5000th 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_,) 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 1/2000th of an inch in length, and the posterior filament 4/2000th, giving a total length of 5/2000th: in the longest and best developed specimens of _Chthamalus stellatus_, the nodular enlargement was much elongated and spindle-shaped, and not above half the diameter it had in the earliest stage; the posterior filament (measured from the front of the enlargement, this consequently being included) was 5/2000th in length, and the front part only 1/4000th, giving a total length of 11/4000ths of an inch. These observations agree pretty well with Kölliker's;[47] but this author states, that perfectly developed spermatozoa are absolutely without any nodular enlargement: if this be the case, I have never chanced to see the spermatozoa in their perfect condition. Mr. Bate, also, figures some (Pl. 29, fig. 7, _c_) in this state, without any enlargement. [47] 'Annales des Sciences Naturelles,' (2d series), tom. xix, p. 348. Kölliker refers to Wagner's paper on the same subject, in Wiegmann's 'Archiv,' 1835, part ii, pl. iii, fig. 9. He also refers to Von Siebold's observations. Mr. C. Spence Bate has figured, in the 'Annals and Magazine of Natural History' (vol. viii, 2d series, 1851), the spermatozoa of _Balanus balanoides_, _perforatus_, and of _Verruca (Clitia) Strömia_, and of these I have given copies, Pl. 29, fig. 7.