ON APPKNDICULARIA FLABELLUM 459 



but it is assuredly closed at both ends. Its closed and rounded 

 proximal extremity is readily seen, and I feel confident that there is 

 no such communication between the heart and the interior of the axis 

 as Gegenbaur supposes. In the individual already referred to, in 

 which the spermatozoa were effused into the general current of the 

 blood, none entered the axis of the caudal appendage. 



The discovery of the external openings- of the pharyngeal canal 

 and of the true nature of the supposed " ciliated cleft," appears to me 

 to possess peculiar interest, in that it eliminates those structural 

 peculiarities hitherto supposed to exist in Appendicularia, which were 

 in discordance with the general plan of the Ascidians. That an 

 Ascidian should have apertures in its pharynx, establishing a com- 

 munication between its cavity and the sinus system, would be a great 

 anomaly ; but that Appendiadaria, being an Ascidian, should possess 

 a ciliated sac, and that the wall of its pharynx should possess ciliated 

 apertures or stigmata, establishing a communication between its cavity 

 and the exterior, independent of the mouth, is only a strengthening of 

 the evidence of its truly Ascidian nature. 



Again, while the existence of these apertures establishes further 

 most interesting relations of representation between Appendicitlaria 

 and the larvae of Ascidians, especially of Phalliisia, it cuts away all 

 ground for any supposed relations of affinity between the two. In 

 Phallitsia, it is true, as Krohn has shown, the cloaca is at first double, 

 and each half, which might be regarded as the equivalent of the outer 

 half of the pharyngeal canal in Appetidiciilaria, opens by an inde- 

 pendent aperture ; but then the anus, instead of opening externally, 

 terminates in one of these cavities. The enormous size, coarse ciliation 

 and very small number of the pharyngeal stigmata in Appendiadaria, 

 too, are wholly unlike anything larval. 



The development of the nervous system and of the organs of sense 

 is quite opposed to the supposition that Appendicularia is a larval 

 form ; and, in answer to Leuckart's suggestion that developed 

 spermatozoa and ova are found in insect larvae, I would urge that, in 

 these matters, it is hardly safe to judge of one class by analogical 

 arguments drawn from another. I am not aware that such early de- 

 velopment of the reproductive products has ever been observed in any 

 mollusk. 



The discovery ot the true branchial apertures in Appendicularia 

 appears to me to bear no less importantly upon the moot question of 

 the homologie of the Tunicata and Polyzoa, by removing all doubt as 

 to the truly pharyngeal nature of the branchial sac in the Ascidians. 

 But, if it be a pharynx, it cannot be the homologue of the conjoined 



