12 COMMISSION OF CONSERVATION 



European oyster, on the contrary, the eggs, after passing from the ovarv, and oviduct, 

 are retained for some days in the mantle cavity of the mother, v/here development 

 progresses through the oosperm, embryo, and young shell-bearing stages that are also 

 capable of locomotion, the latter being finally passed out into the sea as actively swimming 

 larvae, protecting themselves and finding their own food. These, while retained within 

 the mother, may be excusably called embryos, but not larva; after they take to an in- 

 dependent life they are larva;, not embryos. The term 'spat" appropriatelv applies to 

 the succeeding fixed condition as resembling spit (i.e. spittle). 



In accordance with the preceding, it may be pointed out that the word "embryo- 

 logy" is itself less suitable as a title for the present paper than the much broader term 

 "ontogeny" which, because of its unfamiliarity, is often supplanted by the expression 

 "developmental history," or simply "development." 



It is impracticable to procure eggs, oosperms, or embryos as thej^ 

 occur in the natural course of development in the sea; to obtain them in 

 numbers and with facility it is necessary to turn to artificial means, be- 

 ginning with sexually ripe male and female oysters. 



The Sexes. — The oysters of eastern Canada are dioecious or unisexual, 

 i.e., there are two sexes, every individual being either male or female. 

 Males and females cannot be distinguished externally. To determine the 

 sex it is necessary to sacrifice the life of the individual by breaking apart 

 the two valves of the shell. After some experience it becomes possible in 

 most cases to recognize the sex by observing the surface of the abdomen, 

 provided always that the individual is sexually mature and its repro- 

 ductive elements are approaching ripeness. At such a time the abdomen 

 presents a plump and milky appearance, whereas in immature specimens 

 and those that have already spawned, it is either shrunk, flabby and 

 opaque, or else it is distended, watery and semi-transparent. Coarse- 

 ness of the ramification of ducts on its surface, as well as a creamy colour 

 and distinct granulation, are indicative of femininity. By stroking the 

 abdomen backwards it is often possible to squeeze spawn or milt out of 

 the opening of the oviduct or sperm-duct, in much the same way as fishes 

 may be "stripped." In case the specimen is not quite ripe it is necessary 

 to puncture the abdomen or one of the larger ducts and extract a little of 

 its contents. In viewing this again it is generally possible to decide with 

 the unaided eye, for eggs in mass are yellower in colour and coarser in 

 granulation, while spermatozoa are whiter, with a very fine or more homo- 

 geneous appearance. But the surest way, as well as the most expeditious, 

 is to transport on the point of a scalpel a small portion of the spawn or milt 

 to a drop of water on a slide and observe it under a microscope. Ripe 

 eggs or sperms readily separate and float out into the water, facilitating 

 a clear view of their size, shape, structure and activities. From their 

 characters the sex is determined. 



Eggs and Sperms. — Under a low power of the microscope, eggs 

 (Plate V, fig. 1) appear to be somewhat large objects, of a 

 spherical, oval, pear-shaped or even more irregular form. The more 

 spherical ones (fig. 3)) measure about .05 millimetres (= 1/500 inch) in 

 diameter, each limited by a membrane (vitelline membrane, cell-wall, 



