254 Royal Society. 



trastapedial process, and, extending inwards as mediostapedial and 

 interstapedial, articulates with the stapes, developed by segmen- 

 tation from the outer wall of the auditory capsule. The stylo-hyal 

 is dislocated and becomes connected -ndth the auditory capsule 

 below the stapes (opisthotic region). 



In the Bird, the hyoidean arch i*emains distinct from the man- 

 dibular. Whilst in its primordial condition it coalesces by its 

 incurved apex with the auditory capsule in front of the promon- 

 tory, before the stapedial plug is segmented. It then chondrifies 

 as three distinct cartilages — an incudal, a stylo-hyal, and, distally, 

 a cerato-hyal. The stapes becomes free from the aiulitory capsule, 

 but remains united vnth. the cartilaginous part of the incus (medio- 

 stapedial) ; the ascending part is largely fibrous (suprastapedial), 

 and the part loosely attached to the mandibular arch is the elon- 

 gated extrastapedial. The short stylo-hyal afterwards coalesces 

 with the body of the upper or incudal segment by an after- 

 growth of cartilage (the interhyal tract) ; a long membranous space 

 intervenes between it and the glossal piece (cerato-hyal.) Thus 

 the " columella " of the Bird is formed of one periotic and three 

 hyoidean segments. 



In the Pig, the hyoidean arch is distinct, but articulates closely 

 with the mandibular; its upper segment ( hyo-mandibular) is con- 

 verted into the incus, and becomes connected with the stapes. The 

 stylo-hyal is dislocated and coalesces with the opisthotic region of 

 the auditoxy capsule. 



December 18, 1873. — Joseph Dal ton Hooker, C.B., President, in 



the Chair. 



" On the Nervous System of Actinia" — Part I. By Professor P. 

 Martin" Duncan, M.B. Lond., P.E.S., &c. 



After noticing the investigations of previous anatomists in 

 the histology of the chromatophores, the work of Schneider and 

 Kotteken on these supposed organs of special sense is examined 

 and criticised. 



Agreeing with Hotteken in his description, some further in- 

 formation is given respecting the nature of the bacillary layer and 

 the minute anatomy of the elongated cells called " cones" by that 

 author. The position and nature of the pigment-cells is pointed 

 out, and also the peculiarities of the tissues they environ. It is 

 shown that the large retractile cells, which, according to Eot- 

 teken, are situated between the bacilli and the cones, are not 

 invariably in that position, but that bacilli, cones, and cells are 

 often found separate. They are parts of the ectothelium, and 

 when conjoined enable light to aii'ect the nervous system more 

 readily than when they are separate. Further information is 

 given respecting the fusiform nerve-cells and small fibres noticed 

 by Rotteken in the tissue beneath the cones ; and the discovery of 

 united ganglion-like cells and a diffused plexiform arrangement 



