190 HUXLEY, ON APPENDICULARIA FLABELLUM. 



anomaly ; but that Appendicularia, 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, inde- 

 pendent 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 

 Ap])endicularia and the larv2e of Ascidians, especially of 

 Phallusia, it cuts away all ground for any supposed relations 

 of affinity between the two. In Pliallusia, 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 Appencliculai-ia, opens by an inde- 

 pendent aperture ; but then the anus, instead of opening 

 externally, terminates in one of these cavities. The enor- 

 mous size, coarse ciliation, and very small number of the 

 pharyngeal stigmata in Appendicularia^ 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 Appendicu- 

 laria is a larval form ; and, in answer to Leuckart's suggestion 

 that developed spermatozoa and ova are found in insect 

 larv2e, 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 development of the 

 reproductive products has ever been observed in any 

 mollusk. 



The discovery of the true branchial apertures in Appen- 

 dicularia appears to me to bear no less importantly upon the 

 moot question of the homologis 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 tentacles of the 

 Polyzoa, which are entirely pre-pharyngeal structures. 



Whatever may be the result of future inquiries as to the 

 arrangement of the female organs in Appendicularia, I can- 

 not doubt that in A. Jiabellum we have an adult form in a 

 male state. Whether the female has a totally distinct form, 

 or whether the ova are developed in the same form at a 

 subsequent period (I have observed individuals so young that 

 it is hardly conceivable that the ova should be developed' at 

 an earlier period), is a problem of very great interest, but for 

 whose solution I see no materials at present. Considering 

 the abundance in which Appendicularia occurs on our own 

 shores, the collection of the requisite data ought to present no 



