DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 925 



The arrangement of the hyoidean apparatus and of the branchial arches, in fairly 

 developed forms, is shown in PI. XXV. figs. 1 and 2. 



The hyaline investment of the branchial arch described in the early larval Anarrhichas 

 appears first in the post-larval Gadoid, -£% inch in length. It clothes the cartilaginous 

 branchial arches and the hyomandibular element as a very thin perichondrial layer, which 

 develops very strong blade-like ridges at a later stage (when the fish measures -§ inch 

 in length). These ridges are three in number, one directed dorsally, the other two 

 ventrally, and enclosing an angle in which the branchial vein passes. The central core 

 of cartilage appears to be rapidly diminishing in diameter, and the hyaline investment is 

 very thick. The branchial pinnae now form a double row along the artery of each arch, 

 and they consist simply of folds of mucous membrane, the cells being very large and 

 defined by a thin external membrane. Delicate cartilaginous supports appear as thin 

 rods projecting from the arch, but not, however, as outgrowths from it. In the post-larval 

 gurnard, T 5 ^- inch in length, these features are well marked, and in Cottus scorpius, -§ 

 inch in length, the details are even more readily made out ; the hyaline deposit is not 

 very thick, nor does it show any indication of the ridges described above. Outside the 

 hyaline layer clothing the cartilaginous arch is an investing connective-tissue stratum in 

 which the arterial and venous trunks lie. It appears to include some muscular elements. 

 An epithelial layer lies externally, and it is much thickened on the anterior or upper side 

 of the arch. Numerous large cells (mucous ?) and vesicles occur in it, and it forms the 

 complex folds of the pinnae. In this form (Cottus) the cartilaginous rod developed in 

 each pinna is very definite. In the gurnard, T \ inch in length, two muscles pass along 

 a part of the first branchial arch on its ventral side, to be inserted on the copula (basi- 

 branchial) of that arch. Before reaching the point of insertion the two muscles lie close 

 together, and in the interval an upright plate of hard hyaline tissue is deposited ; 

 anteriorly it sends out two horizontal plates from its ventral margin, and has in transverse 

 section the form of an inverted T. The branchial artery is very well developed at 

 this stage, having a dense external tunic, within which is a thick fibrous and muscular 

 layer, with longitudinal fibres in separate bundles internally ; these cause ridges in the 

 epithelial lining, and in transverse section they project boldly into the lumen of the 

 vessel. In oblique sections along the branchial arches of a post-larval Gadoid, ^ 

 inch in length, it is observed that the pinnae of one side of the arch are not placed oppo- 

 site those of the other side, but alternately, each with the central cartilaginous support 

 described above. 



Renal Organs. — Just behind the point where the notochord commences, and below 

 the large basilar plate in the larval Anarrhichas of 17th January, cellular glands appear 

 in the space between the parachordals and the roof of the pharynx. The glandular body 

 on each side shows certain empty spaces around it, and lies beneath the auditory vesicle. 

 It is composed of rather large nucleated cells, the whole having at first in vertical trans- 

 verse section an ovoid outline and a thin hyaline investment. The jugular vein lies to 

 the inner side of each, in the connective tissue which fills up the interval between the 



