52 West & West . — Observations on the Conjugatae. 
Specimens of Cosmarium ornatum occasionally have 
irregular pyrenoids, but we have not yet seen more than one 
example in a hundred. Amongst an immense number of 
examples of Cosmarium sphagnicolum , collected in early 
spring in N. Yorks, from moorland pools nearly filled with 
Sphagnum cuspidatum and Ptilidium ciliare , many variations 
were observed in the chromatophores, and the pyrenoids which 
were normally one in each semi-cell, varied from one to three 
(cf. Figs. 34-36). This variability of the chromatophores 
has been described in Penium minutum 1 . 
We figure four cells of Hyalotheca neglecta (Figs. 30-33), 
which show considerable variation in the pyrenoids, but these 
were only found after the examination of a very large number 
of filaments. This irregularity is usually found after rapid 
division, in the same way that abnormality of form is probably 
caused (cf. Fig. 39 of Euastrum didelta). 
This subject is one concerning which much work is yet 
desirable, as several doubtful genera have been founded on 
the structure and arrangement of the chromatophores ; e. g. 
Pleurotaeniopsis , Pleuren teriu m , &c. 
Sexual (?) reproduction is by conjugation and formation 
of zygospores, the conjugating cells generally not being 
differentiated. Double spores are formed in Closterium 
lineatum , Cylindrocystis diplospora and Penium didym oca rpu m , 
and are analogous to those in the Mesocarpeae and homolo- 
gous with those in the Zygnemeae. In some rare cases three 
(or even four) cells have participated in the formation of 
a zygospore 2 . The zygospore is formed between the conju- 
gating cells in all Desmids except Desmidium cylindricum. In 
this species it is formed within the female cell 3 as in Spirogyra 
1 Cf. remarks by Lutkemuller under Docidium baculum. Also Journ. Bot., 
March, 1895, p. 65. 
2 Cf. Staurastrum teliferum in West, Freshw. Alg. W. Ireland, Journ. Linn. 
Soc. Bot., Vol. xxix, PI. XXIV, f. 5 ; Cosmarium rectisporum } W. B. Turner, Freshw. 
Alg. E. India, K. Sv. Vet.-Akad. Handl., Bd. xxv, No. 5, T. X, f. 16 e; also 
Closterimn Pritchardianum , West and G. S. West, Freshw. Alg. S. of England, 
Journ. Royal Micr. Soc., PI. VI, Fig. 5, December, 1897. 
3 Ralfs, Brit. Desm., T. II, f. 1, e, f, g, h, i, k ; Wolle, Desm. U. S., PI. Ill, f. 4 ; 
