REPRODUCTIVE ORGANS OP KUKENTHALIA BOREALIS. 195 



ought to be examined in connection with that of the origin and 

 formation of the whole complicated female organ. As it is 

 difficult to state anything for certain about the age of the 

 individuals hitherto examined, we cannot draw any conclusions 

 from the above-mentioned facts as to the presence of a rudi- 

 mentary brood-pouch, even before the first egg has been laid. 



Another matter of interest is the question of the homology of 

 the brood-pouch in Kiikenthalia. Before deciding it, it ought to 

 be investigated whether the brood-pouch of the species in question 

 arises as a direct projection from the peribranchial cavity, or 

 whether it is possibly formed in connection with the oviduct with 

 which it, when fully formed, is so intimately connected. 



In other Ascidians in which a brood-pouch develops to receive 

 the embryos, it is generally a diverticulum of the peribranchial 

 cavity. 



Though the systematical position of Kiikenthalia borealis will 

 not be discussed in this paper, I will, however, point out that, 

 as the structure of the reproductive organs has been made the 

 chief character in distinguishing the genera belonging to the 

 group Polyzoince, the facts which have been ascertained by this 

 investigation will no doubt be of decisive importance for the 

 systematic position of Kiikenthalia. Comparing the reproduc- 

 tive organs of the last-mentioned genus with those of the other 

 genera of the group, we find that the most striking difference is 

 the presence of a brood-pouch in Kiikenthalia. Though the 

 Polyzoince have been the object of thorough investigation, 

 especially with regard to the structure of the reproductive organs, 

 nothing which corresponds to a brood-pouch seems to have been 

 observed. One might thus conclude that it occurs only in the 

 Arctic form, of which it is consequently characteristic. 



With respect to the genital pouch, the beginning of analogous 

 structures may possibly be found in some genera, though they 

 have not attained the same degree of development as in 

 Kiikenthalia. 



In certain respects, points of agreement may be found between 

 Kiikenthalia and Gynandrocarpa, as, for instance, they agree with 

 regard to the reduced number of the gonads and the structure of 

 the testis (cf. Herdman *, pi. 44. fig. 4). 



NoN-GONADIAL SEXUAL PRODUCTS. 



Though I now venture to maintain that the presence of gonads, 

 testis as well as ovary, in Kiikenthalia borealis is put beyond a 

 doubt, and that it has been proved that ova and spermatozoa are 

 produced in special organs, there are, however, certain facts 

 concerning the reproduction of the species which still seem 



* Herdman, William A., " Report on the Tunica t a collected during the voyage of 

 H.M.S. 'Challenger' during the years 1873-76," Part 2, vol. xiv. London, 1886. 



