RRYOZOA FROM AUSTRALIA. 425 



without avicularia; but since the genus was named by Mr. Busk, I 

 have found a fossil from Australia with them. 



We are yet a long way from fully understanding the avicularian 

 organs ; but as thej^ are so important in palseontological classifica- 

 tion, we may be allowed to examine their function ; and Membrani- 

 pora angulosa, a living form, also found fossil, and allied to a large 

 number of cretaceous fossils supposed to be extinct, furnishes the 

 opportunity of doing so. If we remove the avicularian cover (ony- 

 chocellaire) and examine the membrane which it usually protects 

 and covers, we find first of all a small corneous triradiate mark. 

 This serves for the attachment of muscles, which quickly draw the 

 the membrane down when touched ; but further, near this there is 

 a small disk with a distinct mark in the centre, and this at once 

 reminds us of the rosette-plates of many of the Chilostomatous and 

 Ctenostomatous Bryozoa. This, I take it, is the tactile organ of 

 Mr. Busk (" Avicularian and Vibr. Organs of the Polyzoa," Quart. 

 Journ. Micr. Science, JNo. vi. 1854), and to this the endosarc is 

 attached, and this most important structure of the Bryozoon is thus 

 brought into contact with the exterior. It is well known that the 

 avicularia often retain their power of movement when no living 

 polypides fill the cells ; but it seems that in this way the colonial 

 life can be maintained. 



I have never been able to accept the theory of the prehensile 

 function of the avicularia ; and in the case of Membranipora angulosa 

 it seems almost as difficult to attribute such a function to them as 

 when we find minute avicularia on the dorsal surface of Retepora. 



If Dr. Jullien had made one comprehensive genus, OnycJiocella, I 

 should have accepted it ; but I believe that the eight genera created by 

 him cannot be distinguished, since, in the first place, the shape of the 

 boundary is variable, and, in the second place, the shape of the 

 opesia can scarcely be considered of generic value. I therefore call 

 all the species Membranipora, although feeling that there should be 

 a separation of those with a considerable calcareous expansion*. 



In the same way the genera Selenaria and Lunulites cannot be 

 looked upon as more than provisional, and will have to be broken 

 up; for Lunulites incisa has Schizoporellan characters, while Selenaria 

 maculata has the calcareous expansion and opesial opening of such 

 Membranipora^ as M. angulosa. 



A large number of the slides were broken f on the journey ; but 

 in the majority of cases, from the boxes in which they were found, 

 there was no doubt as to their origin, though, unfortunately, I am not 



* Smittipora I should consider to be Micropore/,, and not closely allied to such 

 a form as M. angulosa. 



t I have already ("Dry Mounts for the Microscope," Journ. Eoy. Micr. 

 Soc. ser. ii. vol. i. pt. i. p. 138, 1881) called attention to the danger of zinc var- 

 nish becoming brittle, so that the mount and ring readily spring from the 

 glass or wood when exposed to the shaking of a railway journey. I also pointed 

 out the unadvisability of using metal rings, and would strongly urge naturalists 

 sending slides a long distance to use gold-size and india-rubber rings on glass 

 slips where practicable. I feel convinced that slides mounted in this way would 

 have stood the journey better than those Mr. Wilson sent over. 



