478 JiEl'OKT OF CO.MMISSIONKK OF FISH AND FISHERIES. [24] 



egg follicle, consisting of but a single layer of cells. At the time of 

 maturation, a fatty metamorphosis of the cells of the granulosa takes 

 place, which ])roniotes the escape of the egg from the follicle. The 

 microi>yle is always an open pore ; it has a very wide external open- 

 ing and 51 very narrow inner one. The latter ends on an internal prom- 

 inence of the egg-membrane, which is a zona radiata. The lumen of 

 the internal micropylar opening is so constri(!ted that not more than a 

 single spermatozoon can pass through at cue time, as was first ob- 

 served by His in the salmon. 



"It is well known that the eggs of many bony fishes adhere to fixed 

 objects as soon as they fall into the sea-water. This is not always ac- 

 complished in the same way. In Hcliasis, Gohiiis, BlcnniuH^ Belone, etc., 

 this is accomplished by long filaments, excrescences of the zona ra- 

 diata, which are not divstributed over the whole of that structure, but 

 which arc found only on certain portions; viz, in the vicinity of the 

 micropyle. In the herring and Crenilahrus the whole of the surface of 

 the egg is covered with an adhesive material. In the case of all ova 

 which attach themselves by these contrivances, the zona consists of two 

 layers, an inner and an outer one, the latter being adhesive, and split 

 off from the former to eml)race the whole Qgg, or is developed in the 

 form of fibers, processes, and similar appendages. In contrast with such 

 forms, those ov^a which float or sink to the bottom, of their own weight, 

 do not seem to have such a differentiation of the zona into two layers. 

 It is highly probable that the zona is a secretion from the surface of 

 the ovarian egg, and that it is to be regarded as a vitelline membrane. 



"The primordial ova consist of a homogeneous mass, coagulable 

 in acetic acid, when it becomes granular, and they inclose a large nu- 

 cleus and a single large nucleolus. In very young ova, of which the 

 contents are similar to the foregoing, several nucleoli may already be 

 discerned in the nucleus. In the ova designed for the next brood, the 

 yelk corpuscles are gradually developed, until they finally occupy the 

 whole mass of the egg except the space taken up by the nucleus, and 

 only the small spaces between the granules .and corpuscles are filled 

 up by the protoi)lasm still present. The yelk granules and corpuscles 

 consequently appear to be developed at the cost of the contained pro- 

 toplasm of the egg. The cells of the granulosa! Avere never observed to 

 give off' protoplasmic processes passing inwards into the egg through 

 the pore-canals. 



" In the foregoing stage all of the eggs are dull and o])a(pu^ ; even 

 the eggs of If^corpwna, Jidis, Scrramts, and F'lcrafifer, of crystalline trans- 

 parency at maturity, pass through the same opaque stage of ovarian 

 development. In the very large nucleus the nucleoli continue to mul- 

 tiply. 



"Towards the time of maturity, the nucleus begins to move from its 

 original central position to the periphery. During its change of jmsi- 

 tion, the smooth, tightly distended nuclear membrane commences to 



