on the Polyzoa. 153 



genus. Further investigation of some of the * Challenger ' 

 species will be needful before we can safely determine their 

 systematic place. 



An interesting question arises as to the relation between 

 the families of the Adeonidfe and Microporellidse. 



Busk has placed them wide apart in the system ; but the 

 links between the true Adeonce and the Microporellce are (to 

 say the least) far from unimportant, and if it should appear 

 that, on the whole, there are grounds for referring them to 

 distinct families, the affinities which connect them should be 

 fully recognized in our classification. The shape of the orifice 

 and the special suboral pore are important characters which 

 they share in common. Busk, indeed, was of opinion that 

 the pore of the Adeonce " differs widely in nature from the 

 lunate pore of J/ic^-ojoore/^a &c.'^ ('Report,' p. 178) ; but he 

 has not stated the grounds of his opinion. Both of them are 

 special openings into the cavity of the cell, and probably sub- 

 servient to the same function. The mode of their development 

 must be substantially the same. The pore of Microporella is 

 in some cases lunate, in others round, in others again elon- 

 gate ; it is sometimes fimbriated, sometimes simple. The 

 lunate form is due to the presence of a small rounded flap, 

 which projects over the opening and partially closes it. This 

 appendage is probably protective, like the marginal teeth, but 

 has no peculiar significance. I can find nothing in the struc- 

 ture or development of the Microporellidan pore which indicates 

 a difference in " nature " between it and the pore of the 

 Adeo7ice. The two are homologous structures, with the same 

 general characteristics. 



If we examine the points indicated by Busk as character- 

 istic of the family of the Adeonidae, with a view to determining 

 their precise significance, we shall find, I think, that the 

 presence of ooecial cells, or rather of cells specially modified 

 for the discharge of the reproductive function (gonoecia), is the 

 only one that is in any sense distinctive. The avicularian 

 cells are far from uncommon, and are met with in many 

 genera. In such a form as Schizopoi-ella serrati7nargo, mihi, 

 they bear the closest resemblance to those of Adeona. A 

 familiar example of them is found in the British Schizotheca 

 Jissa, Busk. 



The special pore, as I have shown, is essentially identical 

 with that of Microporella. The peculiarity in the avicularian 

 mandible could hardly be accounted a character of primary 

 importance, even if it were confined to this family ; but 

 "Waters has sliown {loc. cit.) that it occurs in several species 

 beyond its limits, which are referable to distinct genera. The 



