Si8 



FRESH-WATER BIOLOGY 



The female is viviparous and produces myriads of young. The 

 larva at birth (Fig. 814, a) has an awl-shaped tail equal to one- third 

 the total length ; no trace of the adult lips are seen ; the esophagus 

 is simple, as also the intestine, and a single cell is the only trace of 

 genital organs present. A boring spine lies dorsal to the mouth. 



Fig. 814. Development of CamaUanus lacustris; a, youngest stage of larva; b, second stage from body 

 cavity of Cyclops; c, at end of second stage showing jaws forming; d, third stage with larval jaws complete. 

 Magnified. (After Leuckart.) 



The larva soon gains entrance to a small aquatic animal (e.g., 

 Cyclops) through the mouth and bores its way into the body 

 cavity where the first molt occurs. After this the worm (b) has 

 grown in size, lost its long tail in part and acquired a bipartite 

 esophagus. A period of growth follows towards the close of which 

 the Hps of the adult are laid down (c) and the second molt dis- 

 closes an oral armature (d) which though smaller and differently 

 marked than that of the mature worm, yet displays its likeness 

 even to the beginning of the dorsal and ventral labial tridents so 

 conspicuous in the adult CamaUanus. The genital area is still in- 

 significant and the tail carries three small spines near the tip which 

 survive in the adult female only. The double esophagus is fully 

 differentiated even to the valve cells at the lower end and the 

 nerve ring is well developed. 



In summer these changes require only 3 days but in winter they 

 may last 3 weeks. No further change ensues until the parasites are 

 brought into the alimentary canal of a suitable fish host. Here 

 set free from the larval host by digestion, the worm grows rapidly 

 to I mm. in length, molts and assumes the sexually differentiated 



