96 I'AUI. I,ØYMN<.. M.-N. Kl. 



processes, from d.irk hiovvn to |)iirc wliilc 1 \\i- huibous swelling below 

 thr ti)) of the iliii)o|)li()res has never been observed so conspicuous nor 

 with th( jxciiliar lorm described by A. & H. It seems in our specimens 

 to be lorined b}- contraction of tiie upper part of the rhinophores. Never 

 more than 21 teeth in the radiila. Number oi' denticles as a rule 4 — 8, in 

 some specimens clearly defined, in others only like fine lines in the tooth 

 plate, the smallest and youngest specimens having as a rule larger and more 

 numerous denticles than older ones. 



The species has never been foutid in the Drobak Sound on the sponge 

 Holichondria pmiicca of which a great number exist, but alwa\-s on algae 

 among hydroids. 



The spawning period extends from August to October. 



Biological Summary. 



In the Drobak Sound most aeolids are found on algae and hydroids 

 in shallow water (2 — 15 metres). Only Acolidia papulosa was found craw- 

 ling on stones on the beach. 



Several species seem to have no constant spawning season. Most ot 

 them spawn in spring, summer or autumn, rarely in winter. According to 

 my observations the spawning proceeds in the following way: When the 

 eggs are laid on a flat support the animal crawls forwards turning con- 

 tinually to the left so that the string of eggs takes the form of a perfect or 

 imperfect coil or a spiral. If the çtgg string is spiral shaped, the spiral is formed 

 from within, and the curl is counterclockwise. If the animal is some way 

 or other prevented from finishing the spawning in the usual manner, it 

 may adapt herself to the new conditions. One specimen of Facclina drum- 

 moudi was thus compelled to turn to the right and to form the last half 

 of the egg-string spiral from without inwards. 



.When the eggs are deposited on seaweed, the animal also crawls for- 

 wards but does not turn in any fixed direction. I have never seen any 

 nudibranch going backwards while depositing eggs like that described by 

 A. & H. 



Several facts appear to indicate that the duration of life is only about 

 a year, thus for instance the rate of their growth. (See table of Coryphclla 

 rufibranchialis) . The animals seem to die after depositing the eggs. 



During the 2 — 3 years of m}' investigations I have been able to 

 prove considerable variations within the nudibranch fauna. Aeolidiella^ glaiica 

 which had been found in masses every year (1916 — 20) during the spaw- 

 ning season, did not appear at all in 1921. While in this year enormous 

 numbers of Facclina drtttiiiuoudi appeared in the same place and at the 

 same time previously characteristic of Ac. glauca. Einblctonia pallida was 

 found onl}' in 1920, neither before nor after, etc. 



