1889.] On the Early Development of Lepidosteus osseus. 109 



acquaintance of fishermen on the St. Lawrence who assured me, and 

 I often verified the fact with my own eyes, that each one of them 

 catches from 60 to 70 sturgeons per week. Many attempts were 

 made to fertilise sturgeon eggs, but all were unsuccessful, probably 

 the season was too early. Lepidosteus material was fairly easily 

 obtained, and a large collection of embryos and many adult fishes 

 were secured. 



I owe my thanks to the Government Grant Committee of the Royal 

 Society, for the substantial grant which enabled me to defray the cost 

 of collection, &c, of the material used in the following investigations. 



Tt is proposed to give an outline of the development of Lepidosteus 

 during the first three weeks of its life ; by the end of this time 

 pretty nearly all the organs are developed, and the larva has acquired 

 many of the adult characteristics. The early development, i.e., that 

 of the first four days, is very difficult of investigation, far more so 

 than that of Amphibia and Marsipobranchii. The reason of this 

 lies with the yolk, for that outside the embryo gives rise to technical 

 difficulties, while that which fills all the cells renders everything 

 blurred and indistinct. Fortunately, much can be made out by means 

 of surface views, and these help very materially in rendering an 

 interpretation of the sections possible. 



The Lgg. — I have little to add to Balfour and Parker's account. 

 As they state the ripe eggs are spherical bodies of 3 mm. in diameter. 

 The egg-shell is composed of two parts : (1) externally a layer of 

 pyriform bodies, and within it (2) a zona radiata. ISTo micropyle 

 could be detected. 



The pyriform bodies are certainly modified cells, each with the 

 remains of a nucleus at its outer end. • These modified cells have 

 degenerated into a sort of glue, which causes the excessive stickiness 

 of the newly laid eggs.* Such a layer, though less developed than 

 here, is characteristic of the eggs of sturgeons and Petromyzon. 



In the ovarian egg these " pyriform bodies " are probably nutritive 

 cells to the ovum, for their outer ends near the nuclei contain a 

 number of minute yolk particles. 



The inner egg membrane is not composed of two layers either in 

 Lepidosteus or in the sturgeon. It is a simple zona radiata, the striae 

 reaching to the innermost portions of the membrane. The division 

 into two layers, sometimes seen, is the optical effect of thick sections. 



Within lies the egg proper. It consists of an outer protoplasmic 

 layer containing small yolk particles, and a central yolk mass, free 

 from protoplasm, and made up of much larger yolk plates. There is 

 a large germinal vesicle with membrane, the vesicle containing a 

 rather large number of chromatin bodies. 



* In alkalies, baryta, and lime-water tke egg-shell swells up, and the two latter 

 reagents are valuable allies in getting rid of the egg membranes in young stages. 



