Prof. R. Kossmann on the Ciyptonisciclre. 9 



self-fertilization }30ssible in cases where a meeting of two 

 individuals can occur only with difhcultj or not at all. Now- 

 self- fertilization is certainly in other respects injurious ; as 

 intensified incestuous breeding it has an exceedingly corrupt- 

 ing influence upon the organization of the race. It is no doubt 

 for this reason that in sonic hermaphrodite groups of animals 

 the habit of mutual fecundation has been brouglit about. In 

 this certainly the above-mentioned advantage disappears ; the 

 contact of two individuals is, as in other cases, necessary. 

 On the other hand, another advantage results from it, namely, 

 when the comparatively obstructed chance of contact does 

 occur, then at least two individuals are fecundated, and 

 consequently there exists twice as much probability of the 

 preservation of the species as if the animals were not herm- 

 aphrodite. 



But if in this way hcrmaphrodism with mutual fecundation 

 may in certain species replace that with self-fertilization with 

 favourable results, this applies only to such as move with 

 difficulty and not to sedentary species. In the latter, contact, 

 and consequently mutual fertilization, is impossible. Here 

 therefore we must rest satisfied with self-fertilization, if the 

 animal were really sedentary during its whole existence. But 

 this is the case in no animal proceeding from an c^g j and all 

 animals proceed from an Qgg^ if not in every generation, 

 nevertheless in generations recurring regularly after a certain 

 time. 



From this it follows thivt even in animals which become 

 sessile contact may take place, always supposing that one of 

 the two individuals is not yet sessile. During this contact 

 they might fertilize each other, if both kinds of sexual organs 

 were already developed in both. This, however, for econo- 

 mical reasons is usually impossible ; for parasites, at least, it 

 is attachment that usually secures that quantity of nutriment 

 which is necessary for the egg-production ; and, on the other 

 hand, parasites generally require for the maintenance of their 

 species such a colossal fertility, that the egg-formation of 

 itself deforms the body and compels it to become attached. 

 Hence, with special exceptions, it is not well possible that 

 the free-moving individual should already possess ovaries ; 

 consequently neither a mutual fertilization nor the one-sided 

 one supposed by Fraisse can be accepted as taking place 

 between two free-swimming animals. On the other hand, 

 the animal may well be capable of the production of the 

 semen, of which no great quantity is necessary, even before 

 the commencement of adhesion, and thus the protaudry above 

 described would be brought about. An advantage over the 



