TRANSACTIONS OF THE SECTIONS. 87 



last, a portion of this particular sponge was lacerated and partially detached from 

 the shell on which it was located. The injury was gradually repaired, and in six 

 weeks afterwards the sponge was as firmly coherent and attached as before the 

 accident. The inhalent and exhalent processes went on chiefly at night, or when 

 the aquarium was darkened. Dr. Bowerbank, to whom some of the other speci- 

 mens were sent for identification, pronounced them to he Halichondria suberea 

 (Johnston), Hymeniacidon suberea (Bowerbank), and stated that "he had never 

 known this species to develope itself in a vivarium before, its usual locality beinf 

 on shells, &c, seven to ten fathoms deep, and he had only once found it between 

 tide marks at Tenby.*' In the month of July last (two 'years after being taken) 

 the sponge had attained the size of a bean, but died about this time, apparently 

 from the effects of excessive confervoid growth, which prevented the free action o'f 

 the oscula and pores. These facts are recorded as an evidence of the great practical 

 value of the marine aquarium as an instrument for the study of similar phenomena 

 connected with marine zoolog-v. 



OJ ' 



Mr. W. R. Hughes, F.L.S., exhibited in an aquarium specimens of Lepidoyaster 

 bimaculatus and L. cornubiensis. The first named is one of the smallest of British 

 fishes, and one of the most attractive tenants of the aquarium. It is somewhat 

 tadpole-shaped, does not exceed two inches in length, the colour is a delicate pink 

 slightly speckled, but is subject to great change, dependent perhaps on the passions. 

 The eyes are of a beautiful colour, not unlike (if such can be supposed) living 

 opals set in an areola of burnished gold ; and they probably have double vision, in 

 consequence of the optic nerves simply crossing in tbeir transit to the brain without 

 any commissural communication. A curious feature and distinctive'character of 

 the genus is that they have the power of attaching themselves and firmly adhering 

 to stones and old shells at the bottom of the sea, by means of a sucker composed 

 of the union of the pectoral and ventral fins, and consisting of two cartilaginous 

 plates surrounded by a fringe. The movement of this sucker is effected by largely- 

 developed muscles springing from the vertebral chain. 



On the Homologies of the Lower Jaw, and the Bones connecting it with the Slull 

 in Birds, Reptiles, and Fishes. By Dr. Gr. M. Htjmphrt, F.B.S. 



After pointing out the features which characterize the lower jaw in mammals 

 on the one side, and oviparous animals (birds, reptiles, and fishes) on the other, 

 showing that in the former it invariably consists of one bone only, or one on each 

 side, whereas in the ovipara there are three or more bones on each side, Dr. Hum- 

 phry indicated that these differences have relation to the functions performed by 

 the jaw in the respective classes. In ovipara, fishes especially, the oifices of the 

 jaws are chiefly confined to swallowing, which is commonly done with a gulp, 

 without any previous division or mastication of the food, and every facility for 

 swallowing is afforded by subdivision of the bones and the widening the pharynx. 

 In mammals, the jaws being employed in seizing, holding, tearing, as well as swal- 

 lowing food, they are, for the purpose of greater strength, consolidated into one 

 bone, which is firmly connected with the skull. The uniformity of this plan, in 

 spite of certain departures in particular animals from the general functions thus 

 assigned to the j aws, was adduced by the author as an illustration of the important 

 principle in zoology that, though the construction of a part in any class is deter- 

 mined by the general ftmction of the part in that class, yet the same plan of con- 

 struction is found even in those members of the class in which the function is 

 different. 



Dr. Humphry then pointed out that, though the mammalian jaw consists of one 

 bone only on each side, yet it presents certain distinct] and prominent parts — ■ 

 the dentary, the angular, the coronoid, and the condyloid or articular parts — 

 which obviously correspond with the separate bones bearing those names in 

 ovipara, adding that if the dentary, the angular, and the coronoid parts of the one 

 be regarded as homologous with the dentary, the angvMir, and the coronoid bones of 

 the other, there is the strongest ground for believino- that the articidar part of the 

 mammal is also homologous with the articular lone of f j>e bird, the reptile, and 



