98 TOILERS IN THE SEA. 



production of two different kinds of swarm-spores. 

 These two kinds are called isospores and anisospores. 

 The isospores correspond to the ordinary asexual 

 zoospores already described, developing without 

 copulation. The anisospores, on the other hand, are 

 sexually differentiated into female zoospores (gyno- 

 spores) and male zoospores (androspores}. The 

 female, or gynospores, are larger, less numerous, 

 possess larger nuclei, and have a fine filiform net- 

 work. The male, or androspores, are much smaller, 

 more numerous, with smaller nuclei and thicker 

 tubercles. In some cases both kinds are developed 

 in the same individual, but not always. It is pro- 

 bable that these two forms of anisospores copulate 

 with each other, after their exit from the central 

 capsule, and thus produce a new cell by the simplest 

 method of sexual reproduction. But since the same 

 species which produce these sexual anisospores at 

 other times give rise to the ordinary or asexual 

 zoospores, it is possible that these two forms of 

 reproduction alternate with each other, and that they 

 thus pass through an alternation of generations. 



The nutritive materials which these animals re- 

 quire for their support are derived partly from foreign 

 organisms, which they capture and digest (although 

 Dr. Wallich has declared his discredit of this), and 

 partly from the unicellular algae (Xanthella) which 

 live within them. The considerable amount of 



