55 



Salpingceca brunnea Stokes. Cells to which several of these flagel- 

 lates are attached very frequently exhibit a breaking up of the cell 

 contents into eight brownish masses, often of spore-like form, and it 

 is not an uncommon thing to find such parasitized filaments with 

 several empty cells. The eggs of the rotifer Diurella ligris are fre- 

 quently found attached to the filaments of this diatom. The num- 

 ber of cells in the filaments in the silk collections averages 6.4 in 1897, 

 and 7 in 1898, while in the filter-paper collections it averages 3.5 in 

 both years. The numbers per filament range from 1 to 40, and the 

 filaments are wont to be somewhat longer during rapid growth than 

 in periods of decline or minimum. 



Melosira varians Ag. Average number, 148,626 (filter-paper 

 3,455,538). The discussion is based upon silk catches. The species 

 was about equally abundant in 1897 but much less so in previous 

 years. This is a perennial species, reported in every month of the 

 year and in most of the collections. It exhibits two well-defined 

 pulses, a vernal one in April-May and an autumnal one in September- 

 October. The reduction in the minimum intervals varies from sea- 

 son to season and from year to year. It was most pronounced, al- 

 most to suppression, in July and August in 1894, 1895, and 1896, and 

 in December-February in 1896-97 and 1898-99. In other seasons 

 the minimum falls to 1,000 to 15,000. 



The vernal pulse (146,916) appears in 1895 on April 29, in 1896 

 (229,235) on May 18, in 1897 (2,419,200) on May 25, and in 1898 

 (3,164,160) on May 5. The autumnal pulse (150,720) is found in 1895 

 on October 30; in 1896, on September 16 at 378,900; in 1897 there 

 are two pulses, one on August 30 at 738,000, and the other on No- 

 vember 15 at 458,800; and in 1898 one, on October 18 at 348,000. 

 The autumnal pulses are thus much smaller than the vernal ones 

 and exhibit a greater range in the time of their appearance. 



As in the case of many other organisms this diatom also exhibits 

 the phenomenon of recurrent minor pulses at intervals of a few 

 weeks. They range in height from 25,000 to almost 1,000,000, and 

 are largest when found in the proximity of the major pulses. The 

 records are not frequent enough to trace them in all seasons. They 

 appear in January in 1896, 1898, and 1899; in February in 1898; 

 twice in March in 1896; in April in 1896; twice in June in 1897 and 

 again in 1 898 ; in July in 1897 and 1898 ; in August in 1897 and 1898 ; 



