28 Mr Sedgwick, On the Celom and body-cavity of [Nov. 8, 
It is therefore important to determine by the study of develop- 
ment, whether or no the blood-containing body and pericardial 
cavities of the Arthropoda are homologous with the corresponding 
structures of other types, in which they do not contain blood. 
The development of the Arthropodan heart and body-cavity is 
in most cases extremely difficult to follow on account of the large 
amount of food yolk present in the embryos, and we have not, at 
present, any completely satisfactory history of it. 
The development of Peripatus Capensis, which is a true Ar- 
thropod, so far as its body-cavity and vascular system are con- 
cerned, is comparatively easy to follow, and I have been able to 
make out with precision the history of the parts in question. 
The ccelom appears in the ordinary manner as a series of 
cavities, one in each mesoblastic somite. 
The somites, which are at first ventro-lateral in position, soon 
acquire a dorsal extension and the cavity in each of them becomes 
divided into two parts——a ventral part which passes into the 
appendage, and a dorsal part which comes into contact but does 
not unite with its fellow of the opposite side on the dorsal wall of 
the enteron. 
The dorsal portions of the somites early become obliterated 
in the anterior part of the body, but posteriorly they persist, and 
those of the same side unite with each other so as to form two 
tubes which are the generative glands. 
The ventral or appendicular portions persist and retain 
their original isolation throughout life. They give rise to two 
structures— 
(1) to a coiled tube, which acquires an external opening 
through the ventral body wall at the base of the appendage and 
constitutes the nephridium of the adult ; 
(2) to a small vesicle which is contained in the appendage 
and constitutes the internal blind end of the tubular or nephridial 
portion of the somite. (The opening of the nephridium into the 
vesicle is funnel-shaped and is commonly known as the internal 
funnel-shaped opening of the former.) 
From the above account it follows (1) that the ccelom of the 
embryo of Peripatus Capensis gives rise to the nephridia and 
generative glands, but to no part of the body-cavity of the adult ; 
(2) that the nephridia of the adult do not open into the body- 
cavity. 
The body-cavity of the adult consists as is well known of four 
divisions: (a) the central compartment containing the intestine 
and generative organs, (b) the pericardial cavity, (c) the lateral 
compartments containing the nerve cords and salivary glands, and 
(d) the portion in the appendage. 
Of these, without going into details, it may be said that a 
