GROWTH AND BEARING OF FOOD-FISH. 375 



nivorous birds, are especially adapted to this peculiar kind of food. 

 Teeth are entirely absent, those of the pharyngeal bones being re- 

 placed by horny papillae above and horny ridges below. The gill 

 rakers have the form of lamellae running transversely to the gill 

 arches, and the whole pharynx thus forms a filtering apparatus, 

 minute nutritious organisms being prevented from passing through 

 the gill apertures and swallowed, while coarse hard substances are 

 ejected from the mouth. The pyloric portion of the stomach forms 

 a globular gizzard, lined with a tough epithelium and surrounded by 

 a thick and strong muscular layer, and thus similar to the gizzard 

 of the majority of birds. The intestines are also extremely long and 

 convoluted, as, for example, in a common fowl ; and there is also 

 some resemblance to the entrails of the latter in the soft texture and 

 yellowish-green colour. 



The fact that grey mullets feed on Diatoms probably explains the 

 following. On May 9th Mr. Dunn sent me a young specimen | of 

 an inch long, on which there was a tuft of brownish-yellow threads 

 projecting from the side of the head. At first sight it seemed as 

 though an abnormal growth of the gills had taken place. But on 

 examination I found that the tuft was attached by a kind of stem to 

 the ventral edge of the right operculum, and had nothing to do with 

 the gills. Under the microscope the growth was seen to consist of 

 branched transparent gelatinous tubes filled with frustules or cells 

 of a Diatom ; the Diatom itself forms the branching tubes. It is a 

 Schizonema ; the species is probably 8. Dilwynii. It is likely that 

 a frustule of this Diatom had at some time or other passed by 

 accident from the pharynx of the fish through the gill clefts, and 

 had then adhered to the operculum and commenced to grow. 



Breeding of the Poor Cod and Pouting. — Several specimens of each 

 of these two species, Gadus minutus and Gadus luscus^ have been 

 living together in a tank of the aquarium since the summer of 1889. 

 In March of the present year most of them were seen to be swollen 

 with ova, and floating eggs were found in the tank. I was too 

 much engaged to collect a number of the eggs and hatch them, but 

 in order to determine the character of the eggs I squeezed a female 

 of each species on April 8th, and examined the ripe ova which were 

 thus expelled. The eggs of both species resembled those of the 

 cod, whiting, and haddock in all respects except size ; that is to 

 say, the yolk was perfectly homogeneous and without oil-globules, 

 and the perivitelline space, or space between the egg and its enve- 

 lope, very small. The diameter of the egg of G. minutus, including 

 the envelope or shell, was r02 mm. ; that of G. luscus very slightly 

 larger, namely, 1"05 to 1"15 mm. 



