KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 63. N:0 9. 23 



well-preserved material has prevented the continuation of my study of the female 

 organs in Kiikenihalia borealis and other Polyzoids. 



In the Polyzoidce there has been observed in some genera the beginning of a 

 genital pouch, i. e. a sac-like structure, projecting from the body-wall and enclosing 

 the generative organs. In one genus, Kiikenthalia, a genital pouch is fully developed 

 and well marked-off. Homologous structures are also met with in the Botryllids. 

 Both in Metrocarpa and Botryllus the reproductive organs are placed in dilatations 

 of the body-wall, though these cannot be said to form well marked-off sacs. 



In Kiikenthalia borealis 1 a brood-pouch develops from the peribranchial cavity 

 to receive the embryos. In a Botryllid genus, Metrocarpa above described, there has 

 been observed a corresponding organ with the same function and also originating 

 from the peribranchial cavity. Bearing in mind the other points of agreement men- 

 tioned above, I venture to state that the occurrence of the last-mentioned organ in 

 the two groups makes the relationship between them indisputable while also indicating 

 the systematic position of Metrocarpa in the vicinity of Kiikenthalia and its allies. 



The cup-shaped structures, described above in the genus Botryllus, are not met 

 with in the Polyzoids, no analogous structure having been observed in this group. 

 B ut, as has been pointed out before, our knowledge of the last-mentioned family is still 

 incomplete, and an investigation of the organ system in question will in all proba- 

 bility bring forth a number of new facts. For the present, as matters stånd now, 

 the genus Botryllus seems from a systematic point of view to be quite isolated. 



The faculty of budding is common to Polyzoids and Botryllids. As far as I can 

 see, it is a character of great importance, the wide-reaching significance of which 

 has not yet been completely grasped. 



To the above-mentioned points of agreement there should be added the fact 

 that the Botryllids agree with Kiikenthalia and its allies as regards the structure of 

 the dorsal tubercle, the dorsal lamina and the tentacles, and even in respect to the 

 faculty of forming colonies which is a feature of both groups. 



What are now the distinguishing characters between the Polyzoidoz and Botryllidce ? 

 As far as I can see, they consist in the faculty possessed b}' the Botryllidai of forming 

 regular stellate groups, in the formation of a common cloaca and the different de- 

 velopment of the atrial siphon that opens into the common cloaca. In the Polyzoidce 

 the two siphons open independently on the surface. 



As to the first-mentioned difference it should be noticed that the formation of 

 regular stellate groups is not a feature that is common to all Botryllid genera, not 

 being for instance characteristic of Metrocarpa and its allies. Moreover, the faculty 

 of forming stellate groups has been observed even in the Pölyzoidaz, in Chorizocarpa 

 systematica Sluiter 2 , as has been pointed out before by Haetmeyer. Instead of 



1 Äkxbäck-Christie-Linde, A., On the reproductive Organs of the Ascidian Kiikenthalia borealis Gottschaldt. 

 Proc. Zool. Soc. London 1921. 



- Sluiteu, C. Pli., Die Tuuicaten der Siboga-Expedition. I. Abt. Die sozialen and holosomen Ascidien. 

 Siboga-Exped. Bd. 56 a. Leiden 1904. 



