216 H. D. Senior. 



that a vitelline network ai^jjears (Raffaele, '88). Type 1 is also 

 commonly found in demersal eggs (among which the majority of 

 the eggs belonging to Type 2 occur) including shad^ itself; and, 

 finally, although some of the viviparous eggs belong to Type 2(6. g., 

 Zoarces and Gambusia) others^ occur which conform to Type 1. 



Since the difference between the two types referred to can scarcely 

 be said to exist in the earlier stages of development, it is well to 

 define, as exactly as may be, what is considered to be the essential 

 difference between them. In both types the heart pulsates prior to 

 the appearance of free blood corpuscles, and the space between the 

 yolk and the extra-embryonic ectoderm is occupied by circulating 

 blood-plasma. In the type in which a vitelline network occurs (Type 

 2), the blood, which acquires corpuscles comparatively early, is, 

 sooner or later, confined upon the yolk, as elsewhere, in actual 

 vessels.^ In Type 1 no vessels are ever found upon the yolk, the 



Scorpaena, Lepidotrigla aspera, Callionyimis, Mugil (capito?), Gadus minutus, 

 Coris (several species), Merlucius vulgaris, Motella vulgaris, Solea (several 

 species). Rhombus laevis, Arnoglossus, Clupea, Engraulis eucrasicholus, and 

 several undetermined species (RafEaele, '88). 



Hippoglossoides limatoides, Rhombus (Psetta) maximus, Pleuronectes plates- 

 sa, P.cynoglossus, P.microcephalus, P.flesus, P. limanda, Solea vulgaris, Molva 

 vulgaris, Centronotus (Pholis) guuellus, Motella mustela, Gadus morrhua, 

 G. aeglefinus, G. luscus. G. merlangus, G. pollaclius, Lophius piscatorius, 

 Trachinus, Clupea sprattus, Trigla gurnardus, Callionymus lyra (Mcintosh 

 and Prince, '00). 



Fierasfer dubius, Stelaphorus ringens (Eigeumann, '92). 



''Also Pomolobus verualis (pseudobarengus), Roccus americanus, Osmerus 

 (Ryder. '84 and '87). 

 Typhlogobius calif orniensis (Eigemnann, '92). 

 Also Pseudopleuronectes americanus and, doubtless, many others. 



^The examples found on record are Sebastodes auriculatus and Cymato- 

 gaster aggregatus (Eigenmann, '92 and '94). Probably a great many more of 

 the viviparous perches also belong to Type 1. The absence of a vitelline vessel 

 network in both the cases mentioned has been assumed from the figures alone. 

 Through the courtesy of Dr. J. Percy Moore I have had an opportunity of 

 verifying the type of Cymatogaster aggregatus. 



*The arrangement of the vitelline vessels (which are invariably veins, 

 Hochstetter, '87) varies considerably in different species, and these variations 

 can he again classified into sub-types (see Ryder, '82, Wenckebach, '8G, H. E. 

 Ziegler, '87, Hochstetter, '87, Ziegenhagen, '94 and '96). 



