xv, g Shaw: Campbellosphaera 505 



side view, with the gonidia too closely packed to be counted. 

 The two other asexual embryos are still less advanced, but with 

 the entry of the gonidia accomplished. The sexual embryo, the 

 presence of which is the reason for the description of its sisters 

 and mother, is nearer the posterior pole and more advanced 

 in development than any of its sisters. It retains the bullet 

 form, with a sharper and blunter end, and measures 60 by 82 p. 

 The average cell diameter is about 3.6 /*, and the estimated 

 number of cells is 1,250. The reproductive cells are sixteen in 

 number and about 12 and 14 n in diameter. They are arranged 

 in four alternating and intermeshing quartets, distributed in 

 about three-fourths of the length of the coenobial cavity, the 

 anterior quartet being more separated from its neighbors than 

 are the others. 



Another sexual coenobium (specimen 24) with a small number 

 of reproductive cells is shown in Plate II, fig. 12. It is on 

 another slide (No. 12) of the same lot as the type slide. It 

 measures 160 by 170 ft. The somatic protoplasts are about 5 

 p, wide, and the somatic cells about 8.3. The number of cells is 

 estimated at 1,400. The reproductive cells are fifteen in num- 

 ber. Thirteen of them are oogonia of about 28 p, and two, near 

 the posterior pole, are oospores of about 32 p, with the walls 

 as yet only slightly developed. There is an absence of repro- 

 ductive cells in the anterior quarter of the coenobium. 



Material containing a larger proportion of sexual coenobia was 

 collected in a shallower neighboring pond, F, within a stone's 

 throw of pond J. A lot collected about 4 o'clock in the afternoon, 

 September 22, 1915, was fixed in the laboratory at 8 in the 

 morning on the following day. A batch of these, stained with 

 Bismarck brown, saturated with Venetian turpentine, was 

 mounted in abundance on four slides and sparingly on three 

 others. In June, 1919, I looked at all of the specimens on slide 

 1 of this lot, and at about 4 per cent of the area of each of the 

 other mounts. These slides show not only a greater abundance 

 of sexual coenobia of Campbellosphaera obversa, but also a 

 larger proportion of other Volvocaceae, including Volvox afri- 

 canus West, the latter being represented by sexual as well as by 

 asexual specimens. The asexual specimens of these two species 

 are readily distinguishable, but the free female coenobia of V. 

 africanus are very similar to the sexual coenobia of C. obversa 

 in these preparations. 



In this material many asexual coenobia were found containing 

 .asexual and sexual daughters in different numerical combina- 



