Ixxil 
by Professor Owen in his ‘Comparative Anatomy of Inverte- 
brates’ is very suggestive of Mr. Spencer’s view. He says—— 
“On the first appearance of the embryo annelid it usually 
consists of a single segment, which is chiefly occupied by a large 
mass of unmetamorphosed germ-cells. And these are not used 
up, as in higher animals, in developing the tissues and organs of 
an undivided or individual whole, but, after a comparatively slight 
growth and change of the primary segment, proceed in the 
typical orders to form a second segment of somewhat simpler 
structure, and then repeat such formations in a linear series, 
perhaps more than a hundred times. So that we may have a 
seeming individual annelid, consisting of many hundred segments, 
in which a single segment would give all the characteristic 
organization of such individual, except some slight additions or 
modifications, characterising the first and last of the series.” 
He also tells us that spontaneous fission has now been observed 
to take place in almost every order of Annulata; and, in many, 
artificial fission produces two distinct individuals. In some cases 
the compound animal consists of very few segments, three only 
in the genus Chetogaster, the fourth always separating as a 
zooid, and forming a new animal. In the higher Articulata, the 
process of gemmation goes on to a considerable extent in the egg, 
and even afterwards in some cases, but more or less irregularly. 
Thus the larva of Julus is hatched with eight segments, and 
at the first moult it acquires six new ones, which are added 
between the last and the penultimate. 
The gradual fusion of the once distinct individuals into a 
complete unity, is shown in a very interesting manner as we 
advance from the lower to the higher forms. In the Annelida, 
Dr. Carpenter tells us, the spiracles of each segment are separate, 
and do not communicate internally with those of other segments. 
In the Myriapoda they partially communicate, while in the 
Insecta they communicate perfectly by a system of anastomosing 
vessels. The same thing is indicated by the various positions of 
the chief spiracles. In Smynthurus among the Poduride there 
are only two, opening under the side of the head immediately 
beneath the antenne. In Solpugide (Arachnida) they are 
situated between the anterior feet; in some spiders they open 
near the end of the abdomen, in others at its base. The position of 
the mouth and eyes at the anterior extremity of the body, and the 
