xv, 6 Shaw: Campbellosphaera 495 



that of other Volvocaceae. But this resemblance may be more 

 apparent than real. 



DESCRIPTION OF THE TYPE SPECIMEN 



For the type specimen of Campbellosphaera obversa the one 

 shown in Plate I, figs. 1 and 2, has been selected. Of twenty- 

 three photographs of this species available at the time of writing 

 this one best exhibits the characters of the genus and species. 

 It is an asexual coenobium containing four embryos and three 

 gonidia. The specimen was fixed with others from the same 

 source in a chrom-acetic acid solution, washed, passed through 

 gradually concentrated glycerin into alcohol, stained in succession 

 with alcoholic Bismarck brown and alcoholic nigrosin, and 

 mounted with a multitude of others in Venetian turpentine. 



The material was collected from a pond in Pasay, indicated 

 in my notes by the letter J, September 22, 1915, fixed at 11.30 

 in the morning on the following day, and stained and mounted 

 during the ensuing season. The specimen was photographed 

 with a magnification of 100 diameters on May 18, 1916 (the 

 negative was accidentally destroyed after the making of two 

 prints), and photographed again with a magnification of 200 

 diameters on the 23d of the same month. The two photographs 

 show the specimen in the same position but with different levels 

 in focus. Three weeks later, June 15, 1916, the specimen was 

 examined for the purpose of taking descriptive notes and found 

 to be flattened into a discoid form and turned up on edge. Three 

 years later, June 7, 1919, the specimen was found to be almost 

 completely overturned from its position at the time of making 

 the photographs. All it lacks of being completely overturned 

 is that the posterior pole is about 45 microns higher than the 

 anterior pole. The present aspect of the specimen is so nearly 

 an exact reversal of the photographs as to arouse a suspicion 

 that the photographs had been taken on reversed plates. The 

 facts that the two photographs taken on different days agree, 

 and that the specimen was seen on edge, makes it clear that the 

 revolution really occurred. 



The coenobium appears to have been somewhat ovoid in form 

 and measured at the time of photographing about 225 by 275 ^. 

 Three years later it measured about 200 /x wide by 235 ^ long. 

 The shrinkage thus shown to accompany the hardening of the 

 Venetian turpentine seems to have been confined mostly to the 

 cell membranes of the coenobium. 



The protoplasts of the vegetative or somatic cells are round 



