1886.] Peripatus and the Arthropoda. 29 
arises as a space between the ectoderm and the endoderm, 8, c, and 
d as spaces in the thickened somatic walls of the somites. The 
spaces are In communication with each other. 
The heart arises as a part of a@ which becomes separated from 
the rest. Posteriorly it acquires paired openings into the peri- 
cardium. It thus appears that the heart and various divisions of 
the body-cavity of the adult form a series of spaces which have 
nothing to do with the celom. They all communicate with each 
other and seem to form a series of enormously dilated vascular 
trunks, of which the heart is the narrowest and alone possesses the 
property of rhythmically contracting. 
To sum up it appears that the coelom in Peripatus is an 
inconspicuous structure in the adult, and has no connection with 
the body-cavity; while, on the other hand, the spaces of the 
vascular system are but little subdivided, and form the heart and 
various divisions of the adult body-cavity. 
If these results are applicable to the Arthropoda generally, and 
I see no reason, from the similarity of the adult anatomy, to doubt 
that they will be found to be so, we may add the following 
morphological features to those generally stated as appertaining to 
the group: calom inconspicuous, body-cavity consisting entirely of 
vascular spaces. 
In Vertebrates and most Annelids, on the other hand, the parts 
in question are arranged as follows: Body-cavity enturely caelomic; 
vascular spaces broken up into a complicated system of channels 
(arteries, veins, capillaries). 
In most Molluscs, finally, the pericardium alone is ccelomic*; 
the vascular spaces being represented by the heart and the more or 
less complicated system of spaces in the body. 
In conclusion I may point out that Kennel, who has correctly 
described the origin of the body-cavity, has failed to elucidate the 
history of the ccelom in Peripatus. He has also failed to recognise 
the fact that the nephridia do not open into the body-cavity. 
A detailed account of my observations, fully illustrated, is now 
in course of preparation, and will shortly appear in the Quarterly 
Journal of Microscopical Science. 
(2) Note on the ‘Vesicular Vessels’ of the Onion. By S. H. 
Vines, M.A., Christ’s, and A. B. RENDLE, St John’s. 
In investigating the vesicular vessels with the object of deter- 
mining whether or not the transverse walls are perforated so as to 
place the cavities of successive segments in communication, the 
* J infer this from the observations of Ziegler (Zeit. f. wiss. Zool. 41) and others, 
who have definitely traced back the pericardium to a space in the mesoblastic 
bands. 
