100 M. Ussow’s Zoologico-Embryological Investigations. 
distinguished observer unfortunately could neither subject the 
results obtained by Kélliker to a thorough testing, nor de- 
scribe exactly the production of the second germ-lamella 
(parenchymatous lamella*), nor, finally, ascertain the mode of 
formation of the intestino-glandular lamella. Undoubtedly 
Metschnikoff’s observations on the mode of formation of the 
organs of sight and hearing, so superficially and inaccurately 
described by his predecessors, are of great value. 
During my long residence in Naples and Messina I set 
myself, as one of my principal tasks, to investigate as com- 
pee as possible the development of several species of Cepha- 
opoda, or, in other words, to subjeet all previous observations 
relating to this subject to a careful examination, in order, as 
far as possible, to enlarge our exceedingly defective knowledge 
of the embryology of these interesting animals. By the 
direct observation of living embryos in various stages, by the 
employment of the most serviceable method of the comparative 
examination of different sections, and, lastly, by the investiga- 
tion of a formative vitellus (which would afterwards be con- 
verted into the so-called germinal spot and then into the 
embryo) with its parts firmly united, separated in a particular 
manner} from the nutritive vitellus, I have been able to 
follow step by step the whole developmental cycle of several 
forms of Cephalopoda. Some difficulties, which met me in 
this little-followed method of investigation, are fully compen- 
sated by a series of new and interesting facts, repeatedly con- 
firmed by me, which I have succeeded in discovering and 
elucidating. 
I have already succeeded in observing pretty accurately the 
development of the embryo in four species of Cephalopoda, 
namely three Decapods (Sepia officinalis, Linn., Sepiola Ron- 
* Loe. cit. p. 67. 
+ In general terms this method is as follows:—First of all the fecun- 
dated ovum, with its capsule, is laid for from five toten minutes in a weak 
solution of chromic acid, in which the capsule is removed. Then the 
ovum is placed for two or three minutes in fresh water, mixed with two 
or three drops of acetic acid. The chorion is removed in another portion 
of fresh water. The viscid, semifluid nutritive vitellus immediately flows 
out, while the germ, which is already somewhat hardened, falls to the 
bottom of the watch-glass. After the removal of the water the germ is 
carefully spread upon a glass slide, and, after being coloured with carmine, 
mounted in glycerine. The foundation of this whole operation is that the 
germ hardens more quickly than the peripheral layer of the nutritive 
vitellus ; for only in this case will the former separate from all inversions 
of the latter. By its aid I have succeeded in separating the formative 
vitellus fram the nutritive vitellus, the whole of which it surrounded, 
and in making a considerable collection of preparations of various stages 
of development of the Cephalopoda, 
