The fishes when first imported from 

 the south are very sensitive to changes 

 of temperature, shipment, or trans- 

 ference from tank to tank. It is advisable 

 to disturb as little as possible until they 

 have been thoroughly acclimated. 



Another Mollienisia. M. formosa, 

 from Mexico, is a nice aquarium fish, 

 but inferior in color to M. latipinna. 

 The body is greenish gray with greenish- 

 yellow cross-stripes; abdominal region, 

 metallic blue; dorsal and caudal fins, 

 dull yellow with dark markings. In 

 contrast to M. latipinna, the males are 

 smaller than the females. Breeding 

 habits, food and temperature require- 

 ments, the same as M. latipinna. 



Embryology of the Goldfish. 



Plate II. 



W. A l*()V8f:K, ll;inii)i()?i(i. Indiiiiia. 



FERTILIZATION, or as it is some- 

 times called, fecundation, consists 

 of the fusion of two cells. In animals 

 the process is essentially the same in all 

 the classes above the Protozoa. The 

 male and female secrete, one the egg, 

 the other the spermatozoa, the union of 

 which results in the formation of a new 

 individual. In the lower torms of life, 

 the cells may be alike, but in the more 

 developed forms there is considerable 

 difference. The female cell or "egg", is 

 largest and passive, containing nutrient 

 matter for the development of the 

 embryo. The male element, or sperm- 

 atozoon has the power of locomotion 

 necessary to reach the egg. 



The usual type of spermatozoon con- 

 sists of head, middle piece and tail. 

 Superficially, it resembles a tadpole with 

 an extremely long tail in proportion to 

 the head. It is, of course, microscopic. 

 The spermatozoa are formed in a gland 

 of the male called the testis (vernacular- 

 ly, in fishes, the milt, as opposed to the 

 roe of the female). 



The essential phenomenon in repro- 

 duction is the act of impregnation of the 



female cell. With goldfish, the male 

 assists the female in the protrusion of 

 the eggs, simultaneously discharging the 

 spermatozoa. Fertilization is accomplish- 

 ed by the entry of a single spermatozoon 

 into an egg. The egg which, before 

 fecundation, was slightly flattened and 

 unexpanded (Fig. 1 ) now becomes 

 globular. Unfertilized eggs are opaque 

 and whitish in color, soon becoming 

 covered with a fungus, and should be 

 removed. The impregnated eggs are 

 yellowish, becoming darker with the 

 subsequent development of the embryo 

 (Fig. 2). With the entry of the sperma- 

 tazoon, changes take place in the con- 

 tents of the egg, completing the process 

 of fertilization and initiating embryonic 

 development. 



The differentiation and development 

 of the embryo proceeds rapidly, depend- 

 ing, of course, upon the temperature of 

 the water (Fig. 3). The various stages 

 may be readily observed under the 

 microscope, observations being made 

 frequently. The stage shown by Figure 4 

 usually proves most interesting to the 

 lay-observer. At this time the alevin is 

 most active within the egg, and is about 

 ready to come forth. It is possible to 

 see the circulation of the blood; to follow 

 the blood corpuscles through the entire 

 body of the alevin, and their return 

 through the gills. When this stage has 

 been reached, the activity of the alevin 

 soon ruptures the egg-walls, thus begin- 

 ning an independent existence (Fig. 5). 



After leaving the egg, the yolk-sac, 

 still attached to the fry, furnishes 

 svistenance for about a week, during 

 which the fins are developed as shown 

 by Figures 5, 6, and 7. The complete 

 absorption of the contents of the sac in 

 ten days to two weeks, finds the fully 

 developed young fish (Fig. 8) foraging 

 for Infusoria, and beginning the battle 

 that results in "the survival of the 

 fittest". 



