1862.] OF THE BLOOD OF VERTEBRATES, 99 
high authority on a question of zoological affinity) has recently 
arranged this animal among the reptiles. 
Fishes.—The structure of the corpuscle is the same as in the two 
preceding classes. The vesicle in fishes is usually more tender and 
evanescent. There are great variations in the size and shape of the 
corpuscles, as discovered by Professor Wagner, especially in the car- 
tilaginous group. They are largest and oval in the Sharks and 
Skates, and circular in certain Cyclostomes, as Ammoceetes and Pe- 
tromyzon, in which the corpuscles are among the smallest—the dis- 
covery also of Wagner. Their large size in the Common Skate was 
discovered by Hewson. In the Pike I found them generally more or 
less pointed at the ends, though in many other osseous fishes the 
corpuscles are more or less regularly oval, and similar in size to those 
of birds, yet with the disc commonly broader in comparison with its 
length. It may be nearly or quite circular ; and often at least half of 
the corpuscles are thus round, especially a few hours after death, so 
that the short ellipse is almost displaced by the circular form, as 
may be seen in the blood of the Tench. 
The most aberrant corpuscles in the class, as might be expected, 
occur in Mr. Yarrell’s Lancelot (Amphioxus lanceolatus), in which, 
according to the observations of Retzius, Quatrefages, and Miiller, 
they are colourless, like lymph-globules and the blood-corpuscles of 
numerous Invertebrata. But it must be recollected that this creature 
is ranked as the lowest fish by Yarrell, and was in fact described by 
Pallas as a Limax. Professor Kdélliker assures us that there are no 
blood-corpuscles whatever in this fish! It has been found on our 
shores ; and whoever may take up a systematic investigation of the 
blood-corpuscles of the Invertebrata must either begin or end with 
Amphioxus, as their connecting link with the Vertebrata. In the 
Glutinous Hag, Miiller found the corpuscles oval, and even fusiform. 
Zoological Import of the Nucleus. 
In Mammalia we have shown that, during an early period of intra- 
uterine life, the temporary red blood-cell with its nucleus is the ana- 
logue of the permanent or common red corpuscle of oviparous Verte- 
brata, while the permanent or common red corpuscle of Mammalia 
is devoid of any such nucleus. 
To the cursory observer it might seem of little consequence 
whether the red corpuscles of the blood of Man and Mammalia have, 
or have not, a nucleus; and accordingly, up to this moment, the 
question seems to have been commonly regarded as a mere microsco- 
pical curiosity. But when, in 1839 and again two or three years 
afterwards, I fully saw the essential difference in question between 
these corpuscles and those of oviparous Vertebrata (having proved 
the fact by careful examinations of the blood of numberless animals, 
and that in opposition to the then prevailing erroneous statements 
and doctrines), it at once appeared to me as a very essential truth ; 
and subsequent experience has only confirmed this view. In short, 
the fact of this structure of the corpuscles of the two great divisions 
