10 SIDNEY F. HARMER. 



It is believed by many writers that there is no fundamental 

 difference between the larvte of the Ectoprocta and those of the 

 Entoprocta, and that the latter belong to the true Trochospheral 

 type. This view is now adopted by Barrois (4), who admits 

 that the alimentary canal, the oral and aboral surfaces and 

 the ciliated ring are of essentially similar construction in the two 

 groups of larvae, and that the internal sac of the larva of 

 the Ectoprocta is the homolugue of part of the vestibule of 

 the larva of the Entoprocta^. I am in complete accord with 

 this view, but would myself push the agreement between the 

 two types of larvae somewhat further, in endeavouring to esta- 

 blish the homology of a part of the embryo of Alcyonidium with 

 the "dorsal organ" of the Entoprocta. 



Although it is true that in my paper on Loxosovia (5) I 

 suggested that the pyriform organ itself might be the homologue 

 of the brain of the Entoprocta, Lankester, in his article Polyzoa in 

 the Encyclopaedia Britannica (10), has somewhat misrepresented 

 the view then expressed by me. 



In Lankester 's fig. 20 (from Balfour, after Barrois), m ? is 

 the pyriform organ, whilst st. (said to be considered by me as 

 the cephalic ganglion) is the sucker or internal sac, the larva 

 being turned with its dorsal surface downwards. 



By reference to one of Repiachoff's figures^ of Tendra, one 

 of the Cheilostomata, it will be seen that the structure of the 

 embryo of this genus is, as has been already explained, extremely 

 similar to that of the larval Alcyonidium. The pyriform organ 

 {x.), the alimentai-y canal (o., g) and the internal sac {v.) correspond 

 with those of Alcyonidium. The dorsal thickening of epiblast, y., 

 which I formerly supposed to represent the cement-gland of the 



1 The -work just quoted was published simultaneously with my paper On tlie 

 Life-History of PedicelUna (6), and some of the figures in the latter would not 

 have been required had the memoir of Barrois appeared at an earlier date. It will 

 be hardly necessary to consider in detail Barrois' criticisms of my previous results, 

 since certain modifications of the views formerly held by me (especially with regard 

 to the nature of the metamorphosis) which I have explained in my paper referred 

 to, bring me into moderately complete agreement with Barrois on the more impor- 

 tant points on which he does me the honour of noticing my results. 



^ Reproduced iu PI. XX, fig. 22 of my paper on Loxosoiua. 



