DESCRIPTIONS OF GENERA AND SPECIES 279 



only ; but so far as the facts go they show a nearly absolute uniformity. The 

 following are the species in which the sexual forms have been studied : Nais elinguis, 

 N. lacustris, N. serpentina, Dero multibranchiata, and Dero sp. In all of these the 

 reproductive organs are very far forward ; I do not include Uncinais littoralis in the 

 list because there are no data in the account given by BOURNE of the ducts, and it 

 is not certain whether the organs which he describes as testes and ovaries are not 

 the sperm-sacs and ovisacs respectively. 



The clitellum in Dero occupies segments v, vi, vii '. The ventral setae are wanting 

 on the sixth segment which bears the orifices of the sperm-ducts. In the species of 

 the genus Nats enumerated above there are special genital setae on the segments named, 

 which replace the ordinary setae. In all the Naidomorpha there is a single pair of 

 spermathecae in segment v ; in the same segment lie the testes ; the sperm-duct is 

 a short tube which expands into the spermiducal gland ; in N. elinguis the transition 

 between the sperm-duct and the spermiducal gland is so gradual that both structures 

 appear to be one. The ovaries are in the next segment to that which contains the 

 testes ; the ripe ova escape by means of a pair of slits between the sixth and seventh 

 segments. The sperm-sac appears to be unpaired. 



The Naidomorpha are characterized by the asexual mode of propagation as well 

 as by the apparently rarer sexual process. This process has been studied by a large 

 number of those observers who have dealt with the species belonging to this family ; 

 more particularly to be mentioned in this connection are LEUCKART, MAX SOHULZE, 

 PERRIER, BOURNE, and SEMPER. Not having myself investigated the subject I do 

 not attempt any criticism of these various observers, but content myself with a brief 

 description of how the process takes place in the group according to the paper of 

 BOURNE upon the matter. I have furthermore added a short account of a recent 

 memoir by KALLSTENIUS which deals with the same process in the genus Amphichaeta. 

 It is important to notice that the asexual method of reproduction in the Naidomorpha 

 follows a more complex course than in Aeolosoma ; in the latter it is merely division ; 

 in the Naidomorpha there is a growth of fresh segments in the middle of the body 

 of the parent worm. I have elsewhere (below) called attention to an appearance often 

 presented by the earthworm Pontoscolex, which seems to be not unsuggestive of a trace 

 of a similar process in the higher Oligochaeta. 



Budding in the Naidiform Oligochaeta takes place, according to BOURNE (5), in 

 the following way : 



1 STIEHEN says vii-xii for D. rmtltibranchiata, but the epidermis showed no modification ; this part of the 

 body was swollen (perhaps only by genital products?). 



