THALLOPHYTA. 



671 



in the oogonia (fig. 382), and these germinate parthenogenetically. Altlioiigh the 

 sexual organs are still preserved in this group their function has been lost, leading 

 the way to their complete atrophy in many other groups of Fungi. Many members 

 of the group occur upon the bodies of dead insects and fish {e.g. various species of 

 Saprolegnia, Achlya, Aphanomyces). Aphanomyces phycophilus is parasitic upon 

 AlgtB (e.g. Spirogyi-a) and Saprolegnia 

 Ferax upon Salmon, &c. 



About 45 species have been distinguished. 



Chytridiaeece. — Small parasitic aquatic 

 Fungi whose mycelium is almost entirely 

 svanting; they produce characteristic spor- 

 angia which liberate uniciliate swarm-spores. 

 Polyphagus Euglenoi develops a very delicate 

 mycelium, of which the branches become 

 attached to Euglena-cells (fig. 379 ^ two 

 Euglenas are thus attacked), and from the 

 central portion of the mycelium arises a 

 sporangium from which uniciliate swarm- 

 spores (fig. 379*) are liberated. These in 

 turn germinate, develop threads, and entangle 

 fresh Euglenas. Rkizidiomyces attacks the 

 oogonia of Saprolegnias, sending a branching 

 mycelium into their interior (fig. 379^) and 

 producing a pear-shaped sporangium at the 

 surface which liberates numerous swarm- 

 spores. Chytfidium Olla (fig. 380^) pro- 

 duces its sporangia on the oogonia of (Edo- 

 gonimn; its swarm-spores escape by the 

 removal of a lid. 



Over 180 species are known. 



Ancylisiacece. — Very nearly resemble the 

 Chytridiaceaj in mode of life, but differ in 

 exhibiting sexuality. Lagenidium Raben- 

 horstii attacks cells of Spirogyra, &c. The spores become attached to the Spi7'0- 

 gyra-cells, and penetrate the wall (fig. 379 ') by means of a tube which branches 

 about within, forming a lobed, irregular body (fig. 379 2), which may open at the 

 outside, hberating swarm-spores (fig. 379^), or sexual organs may arise inside and 

 fertilization take place. 



14 species have been distinguished. 



EntomophthorecB. — A group of forms almost all of them parasitic on insects. 

 They are adapted to non-aquatic life, and connect the Peronosporeaj with the 

 Zygomycetes. 



The tubes of these parasites having effected an entrance into the body of an 



Fig. Z&2.— Achlya lignicola. 



> Oogonia with antheridia and fertilizing tubes; no fer- 

 tilization liappens, however. 2 An oogonium con- 

 taining egg-cells which have put on cell-walls with- 

 out being fertilized. »and>x400. (After Sachs.) 



