and 28 degrees --3rd day. In our opinion, these numbers are close to the 



truth but understandably err by excessive precision and definiteness. 

 Actually, the process of development of larvae undoubtedly fluctuates con- 

 siderably at the same temperature and conversely the period of develop- 

 ment can be the same under fairly strong fluctuations of the temperature 

 (Bychowsky, 1933). The larvae emerge from the eggs through an aperture 

 which is formed on the upper end of the egg after the falling away of the 

 operculum. The latter is opened due to the slight jars of the larva which 

 is lying in the egg and sometimes only after considerable effort on its part, 

 in a number of cases during the course of two to three hours. Very often, 

 in normal conditions we happened to observe the deaths of larvae of the 

 latter because of the impossibility of opening the egg due to the fact that it 

 was overgrown by certain vegetable or bacterial organisms. As a rule, 

 the little larva formed in the egg normally lies with the head end toward 

 the operculum of the egg. In rare cases we observed the formation of little 

 larvae lying the other way around, and these larvae in a majority of cases 

 were unable to turn around and come out of the egg. The emergence of the 

 larvae usually takes place during the warmer time of the twenty-four - hour 

 period, predominantly in its first half, and with the lowering of temperature 

 it is possible to retard the emergence of fully formed larvae for several days. 



Undoubtedly the illumination of the latter exercises considerable p. 93 

 influence on the emergence of the larvae from the eggs, thus it was possible 

 for us to delay for rather long periods the emergence of the larvae among a 

 number of species of Axine by placing the eggs in a dark place. And we were 

 able to regulate the emergence of formed larvae precisely enough by sw^itch- 

 ing them to a lighted place. 



The larvae which emerge from the eggs move at first almost 

 in straight lines, now accelerating, now delaying their motion. During the 

 time of this first period of their life the larvae are characterized on the one 

 hand by a strongly expressed positive phototropism; on the other hand by 

 the inactive condition of the attaching apparatus because of which they cannot 

 attach themselves to the body of their host. Both these peculiarities repre- 

 sent an important adaptation to the creation of the best conditions of dissemi- 

 nation of the larvae in the water. This period is succeeded after a certain 

 interval by another, and is characterized by the fact that the larvae acquire 

 ability for attachment and that among them the positive phototropism dis- 

 appears or at least is strongly reduced and, for the most part, . the negative 

 phototropism is acquired. During this time, which is the longest in the 

 larval period, the larva swims with undiminished speed but quickly changes 



1 The negative phototropism of the larvae of Diplorchis ranae Ozaki in- 

 dicated by Ozaki (Ozaki, 1935b) is undoubtedly related to the following 

 (second, nobis ) period of the life of the larvae. 



93 



