INVERTEBRATA, CRYPTOQAMIA, MICROSCOPY, ETC. 849 



The form of the primary, and the disposition of the secondary 

 tubules, allows of the division of the organ into two parts ; a superior, 

 in which the primary tubules are contorted, the secondary few and 

 incompletely separated ; and an inferior, in which the primary tubules 

 are straight, the secondary numerous and completely separated by 

 sei^ta. 



In the primary tubule, two regions may be distinguished, differ- 

 ing according to the character of the glandular cells. 



The Harderian gland of birds resembles in structure that of 

 reptiles, but differs wholly from that of mammals, which is a racemose 

 gland. 



There are certain glands which form a transition between the 

 gland in question and the simple tubular gland on the one hand, and 

 the racemose gland on the other. 



Structure of the " Eye-spots " of some Osseous Fishes.*— Dr. M. 

 Ussow points out that the structure of these organs, the presence of 

 which has been noted by a number of zoologists, has never been 

 investigated by any anatomist other than Leuckart (1^64) ; the author 

 himself has ah-eady published some observations on the subject, in 

 which he has demonstrated the metameric character of these organs, and 

 has shown that they are formed on the type of the so-called compound 

 eye, and are provided with simple cornefe. The structures may be 

 arranged in two series ; in one they are accessory eyes, and in the 

 other they form pigmented glands ; the genera ChauUodus, Astro- 

 nesthes, and Stomias present examples of the former, as do Scopelus, 

 Gonostoma, and Mauroliciis of the latter. The organs in question 

 are found on either side of the ventral median line, where they form 

 one or two parallel rows extending from the caudal fin to the first ray 

 of the thoracic fin ; they are placed just below the scales, and they 

 have the form of small pigmented spots, varying in number from 

 sixteen to forty-eight. 



After describing in detail their character and position in a 

 number of forms, Dr. Ussow passes to an account of their structure. 

 Most simple in Astronesthes, they have the form of a biconvex 

 lens, which projects somewhat beyond the surface of the body, 

 and they exhibit the following points: (1) a thin investment of 

 connective tissue which completely envelopes the eye ; (2) a thicker 

 pigment layer, formed by six-sided dark brown cells ; (3) in this 

 there is a circular orifice, which is merely covered by the transparent 

 envelope ; then (4) there is a lens-shaped body which resembles in 

 structure the lens of many Vertebrata ; (5) in the subjacent layer we 

 find transparent hexagonal plates, altogether devoid of pigment, not 

 exhibiting nuclei, but showing a longitudinal striation of their 

 component protoplasm. These cells are arranged concentrically, and 

 the whole of the internal cavity is filled ■ndth a transi^arent watery 

 fluid, which easily coagulates under the influence of reagents. The 

 organs in question appear to be supplied by the rami ventrales, which 

 send fine nerve-filaments to them. We have no space to follow the 



* 'Bull. Soc. Imp Nut. Moscou,' liv. (1879) p. 79. 

 VOL. II. 3 L 



