306 SUMMARY. 



oral face is situated in all cases the mouth, and in the entoproc- 

 tous larvae and Cyphonautes also the anus. It thus appears that 

 Cyphonautes, though the larva of an ectoproctous form, is itself 

 entoproctous a fact which tends to shew that the Entoprocta 

 are the more primitive forms. In all the larvae, except possibly 

 those of the Cyclostomata, there is present on the anterior side 

 of the mouth, in the Ectoprocta on the oral, and in the Ento- 

 procta on the aboral side of the ciliated ring, an organ, to which 

 is attached externally a plume of long cilia. This organ has 

 been identified throughout the series 

 in accordance with Hatschek's view 

 as the dorsal organ or rudimentary 

 bud ; but it is well to bear in mind 

 that this identification is of a purely 

 hypothetical character. 



On the aboral side of the ciliated 

 ring there is present in all the larvae FlG - '33 A - DIAGRAM OF AN 



IDEAL LARVA OF A POLYZOON. 



an organ, which has been called the OT . mouth; an. anus;j/. sto- 

 ciliated disc, which is probably homo- mach; s - ciliated di sc. 

 logous throughout the series. It perhaps remains in the adult of 

 Loxosoma as the cement gland, but not in other forms. 



The Polyzoa present a simple and almost certainly degraded 

 organisation in the adult state ; it is therefore more than usually 

 necessary to turn to their larvae for the elucidation of their 

 affinities, and various plausible suggestions have been made as 

 to the interpretation of the characters of the larvae. 



Lankester 1 has suggested that the larvae are essentially 

 similar to those of Molluscs. He compares the main ciliated 

 ring to the velum, but has ingeniously suggested that it repre- 

 sents not the simple velar ring of most molluscan larvae, but 

 a more extended longitudinal ring, of which the gills of Lamel- 

 libranchiata are supposed by him to be remnants, and to which 

 the Echinoderm larvae with one continuous ciliated band furnish 

 a parallel. 



The foot he finds in the epistome of the Phylactolaemata, 

 and the disc of Rhabdopleura both situated between the 

 mouth and anus, and therefore in the situation of the molluscan 



1 Lankester. "Remarks on the affinities of Rhabdopleura." Quart. J. of 

 Micro. Science, Vol. XIV. 1874. 



