in the Fcetus of Vertebrated Animals. 327 



IV. (From Prevost and Dumas) Ovum of the dog, twelfth day. The 

 primitive trace of the embryo. Fig. 4. Natural size. 

 V. (From the same) Ovum of the same date farther advanced. Fig. 5. 



Natural size. 

 fi. (From the same) Transparent area in the ovum of the Kabbit, with 

 the primitive folds of the spinal canal, commencing vertebrte, &c. 

 1. (From the same) Part of the uterus of a rabbit opened eight days 

 after impregnation. The foetus seen lying on the vascular area 

 of the yolk, or umbilical vesicle, natural size. 



8. (From Baer) Foetus of the dog three weeks, lying on the vascular 



area on its left side, magnified 10 diameters. Fig. 8 •. Section of 

 the foetus, shewing the folds of the spinal canal, intestine, &c. 



9. (From Rathke) Foetus of the pig three weeks, magnified 1 diameter. 

 10. to 19. (From ]Meckel) Represent the changes which the ventricles 



and auricles of the human heart undergo from the fourth week to 

 the third month. 

 20. & 21. Are diagrams copied from those of Mr Owen, to shew the 

 mode in which the upper and lower interaurieular septa, and 

 eustachian valve, are formed in the heart of mammiferous ani- 

 mals. 



(To be continued.) 



On Changes observed in the Cobnr of Fishes. By Mr James 

 Stark. Communicated by the Author. 



Having accidentally observed remarkable changes of colour in 

 some minnows I had kept over last winter, I was induced to 

 make a few experiments, with a view to discover the cause of 

 these singular changes. As no observations of the same nature 

 seem to have been recorded, so far as my reading extends, I 

 take the liberty of transcribing from my notes a short detail of 

 some of the experiments I have made upon the Minnow (Leu- 

 ciscus phoxinus) ; the Stickleback ( Gasterosteus aculeatus) ; 

 the Loche (Cobitis barbatula) ; and the Perch (Perca fluvia- 



t'dis.) 



My attention was first directed to this subject from having 

 transferred the minnows above alluded to into a white basin, 

 for the purpose of changing the water in the glass-vessel where 

 they were usually kept. Having allowed them to remain in the 

 basin for some time, it struck me, on going to replace them, 

 that their colours were less vivid, and the dark spots and bands 



