44 NILS HJ. ODHNER 



another in Dotonidae, a third in Elysioidea, provided that these 

 have not a separate origin from different ancestors, which is 

 not unlikely. 



If w^e compare the genital organs of Dotonidae with dif- 

 ferent types of nudibranchs, we find that Doto represents rather 

 a primitive stage in the following particulars: The female portion 

 of the genital apparatus is provided with a simple distal recepla- 

 culum seminis (or „bursa copulatrix") and an indication of a 

 differentiated vaginal opening, and there is no special communi- 

 cation from this to the oviduct. In this character it differs from 

 all the Dorids and the Ascoglossa, and represents a stage more 

 primitive than that of the Aeolididae and homologous with that 

 of Tritonia, Madrella, Dirona, Pleurophyllidia, Tethys, Bor- 

 nella (diaulic type in the sense of Eliot). Among the Tecti- 

 branchia this type is present in for ex. Doridium and, (some- 

 what more complicated), in Lobiger and Pleurohranchus. As 

 to the male apparatus, this is provided with both a prostata 

 and a vesicula seminalis. Together, these are occuring only in 

 Lohiger; a single prostata or a single vesicula seminalis, which 

 may substitute each other, and certainly in many cases are 

 homologous features, exists in most of the Holohepatica and 

 the Ascoglossa as well as in some primitive Cladohepatica, such 

 as Tethys, Tritonia, Madrella — whereas in others, such as 

 Goniaeolis, Doridoeides, it is absent. Thus this feature cannot 

 be taken into consideration for judging the relations. 



The greatly dilated ampulla of the Dotonidae is met with 

 only in Doridoeides and Coramhe, but a narrower one is pre- 

 sent in many Tectibranchia and Nudibranchia (all Ascoglossa 

 and many Holohepatica and Cladohepatica, but it is reduced in 

 many of the more primitive forms such as Tritonia, Tethys, 

 Madrella, Pleurophyllidia). The ampulla thus seems to be a 

 variable organ which may be reduced, or more or less developed 

 in repeated cases; where it is developed in such a degree as in 



