570 REPORT OF COMMISSIONER OF FISH AND nSHEEIES. [116] 



blast inclosiDg the true vitelline matter of the eggs of birds, reptiles, 

 and Elasmobrauclis which is altogether homologous with the same 

 layer iu the Teleosteau ovum. It is also likely that it has a similar 

 origin iu all of these truly meroblastic forms, iu all of which au extreme 

 permanent displacement of the germinative vesicle also occurs. 



In Fig. E, at Jiy^ the hypophysis or pituitary body is showu as a dor- 

 sal diverticulum from the fore part of the meseuterou. The latter is 

 much depressed from above and expanded laterally at this stage. The 

 origin of the hypophysis from the fore part of the mesenterou in Tele- 

 ostei seems to be pretty well established. 



I see no difficulty in referriug the development of the muscle plates of 

 Teleostei to a i^rocess essentially similar to that seen in Amphioxus, viz, 

 as outgrowths from the primitive hypoblast. A comparison of Figs. H 

 £tnd J may make this clearer. 



28. — The DBVELOPlilENT OF THE EGGS OF THE CODFISH. 



When the ova of the cod have been in the hatching apparatus for 

 some time, various organisms will be found to have attached them- 

 selves externally to the vitelline membrane covering the eggs. Monads, 

 infusoria, and algoe avail themselves of the surface of the Q^g membrane 

 as a nidus upon which to fix themselves, as showu in Fig. 34, where the 

 most conspicuous of these proteges is a bell-animalcule of the genus 

 Vorticella. The monads belong for the most part to the subdivision 

 originally characterized by the late Prof. H. J. Clark, and known as the 

 collared flagellates. There were a few free forms observed which were 

 not identified, however. When these organisms become attached iu 

 considerable numbers to the eggs dirt tends to accumulate on their 

 surfaces, giving the eggs a soiled, bad appearance. The most important 

 of these adhering organisms is a one-celled algous plant or protophyte, 

 club-shaped, with its narrow end fixed to the egg', these are most nu- 

 merous, and they contain brownish protoplasm (phycoxanthine) corpus- 

 cles which are adherent to the cell wall. Eggs kept in the liveliest 

 motion were soonest covered with these unbidden guests. Apparatus iu 

 which there was least active movement of the water did not pollute the 

 surface of the ova as quickly. It may be laid doM^n as a rule that the 

 more violent the motion of the eggs the sooner were they loaded with 

 foreign organic growths, which no doubt has a tendency to interfere 

 with the resi;)iration of the embyro through the egg membrane, as well 

 as to weight the egg so as to make it sink and smother. It is very 

 probable that the accumulation of sediment and organisms upon the 

 eggs may have had a great deal to do with the excessive mortalit;y of 

 the cod ova iu the experiments at Wood's Holl. It caused least trouble 

 iu the apparatus used by Colonel MacDonald, operated by the gentle 

 alternate rise and fall of the water by means of siphons acting inter- 

 mittently. 



On the twentieth day, with the water at 38° Fahr., the young fish 



