Data are presented on the lipid composition of Balanus balanus spermatozoa.

Lecithin is the major lipid and little plasmalogen is present.

The results are discussed in relation to what is known of other spermatozoa, both vertebrate and invertebrate.

Some data on the inorganic and organic constituents of Balanus balanus seminal plasma have been given by Barnes (1962 a, 1963); lipids were shown to be present in the plasma and are a well-known constituent of the spermatozoa of other animals (Mann, 1964). In view of the relatively small amount of data on the detailed phospholipid composition of invertebrate spermatozoa the opportunity was taken during the investigation reported in the previous paper (Dawson & Barnes, 1966) to examine the spermatozoa of Balanus balanus. The results are, however, best presented and discussed separately. The results are given in Table 1.