The experiments which we conducted show that immediately upon emerg- 

 ing from the egg, the larva of Nitzschia possess a strong positive photo- 

 taxis and only with the unfolding of the disc does it change into the nega- 

 tive one, in complete conformity with the behavior of the larva of Dactylo- 

 gyrus which was described by us. At the beginning of their lives the larvae 

 swim with unusual speed and force. Upon hatching from the eggs in salt- 

 shakers (stender dishes or test tubes?, at least some type of experimental container, nobis) 

 they immediately "fly out" from them breaking through the film of the surface tension of the 

 water and sliding along the dry surface of the glass for almost a centi- 

 meter above the water. The larvae retain the ability to infest the host 

 fro 5 to 6 hours and after that they lose it although they remain alive and 

 swim in the water approximately 24 hours. 



15. The development of Benedenia Diesing 



The genus Benedenia (Fig. 196) appears to be the typical repre- 

 sentative of Capsalidae. It is characterized by a powerful development of 

 the two head suckers and the attaching disc. The latter is equipped on its 

 inner surface with septa which divide the disc into one central and 7 edge p. 177 

 sections. The chitinous armature of the disc consists of 14 edge and 6 

 middle hooks. The internal structure of the representatives of this genus 

 is uniform: There is a well-developed intestine with a large number of 

 exterior and interior branches. The sex system has two large testes and 

 a large ovary and the effering ducts open at the sides of the body. 



In 1932, Jahn and Kuhn described the development of B. 

 melleni MacCallum, a parasite of American marine fishes, in considerable 

 detail. Then we studied the development of a second species— -B. derzhavini 

 (Layman) from the gill cavity of Sebastodes schlegeli (Hildendorff) in 

 Vladivostok in June, 1949. For the convenience of comparison of the data 

 obtained we shall first give the information concerning the development of 

 B. melleni in the form of a somewhat abbreviated translation from the 

 work of the authors enumerated above and then the data themselves. 



We must say that we have changed the terminology of Jahn and 

 Kuhn somewhat in line with that accepted by us in the present work. 



"The free-swimming larva of B. melleni (Fig. 197) is about 

 0. 23 mm in length and 0. 06 in width, it is flattened at the anterior end and 

 spindle-shaped at the base with the exception of a narrowing in the region 

 of the buccal opening. The posterior one -third of the larva forms an 

 attaching disc which does not function when the larva emerges and which 

 has the sides folded together. The pharynx is rounded, muscular and p. 178 



located in the anterior part of the middle third of the body. It opens into 

 a very short esophagus which changes into two relatively large intestinal 

 trxinks which extend almost to the end of the body. There are no lateral outgrowths. 



191 



