570 EEPORT OF COMMISSIONER OF FISH AND FISHERIES. [116] 



blast iuclosing the true vitelline matter of the eggs of birds, rei)tiles, 

 aud Elasmobrauchs which is altogether homologous with the same 

 layer in the Toleosteau ovum. It is also likely that it has a similar 

 origin in all of these truly meroblastic forms, in all of which an extreme 

 l)ermaneut displacement of the germinative vesicle also occurs. 



In Fig. E, at hy, the hypophysis or pituitary body is shown as a dor- 

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

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

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

 ostei seems to be pretty well established. 



I see no difiBculty in referring the development of the muscle plates of 

 Teleostei to a process essentially similar to that seen in Amphioxns, viz, 

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

 alid J may make this clearer. 



28. — The development 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 algse avail themselves of the surface of the egg membrane 

 as a nidus upon which to fix themselves, as shown in Fig. Si, where the 

 most conspicuous of these prot6g6s is a bell-animalcule of the genus 

 Vorticella. The monads belong for the most i)art 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 in 

 considerable numbers to the eggs dirt tends to ac(;uinulate on their 

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

 of these adhering organisms is a one-celled algous i)lant 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 in 

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

 surface of the ova as quickly. It may be laid down 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 respiration 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 

 l)robable that the accumulation of sediment and organisms upon the 

 eggs may have had a great deal to do with the excessix'e mortality of 

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

 in 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 



