the term Homology in modern Zoology. 43 
matter of time and labour, but is feasible. Besides the homo- 
logies of the vertebrate skeleton and muscles, I would mention 
the various vascular systems of the Invertebrata as likely to 
be better understood in this manner. The vascular system of 
leeches, with its hemoglobin, is not homogenous with that of 
Cheetopods, though closely homoplastie with it: its relation to 
the nervous system, segment-organs, its development, and the 
nae ancestral relations of the Leeches and Trematodes 
ead to this conclusion. Yet most zoologists would consider 
these two vascular systems homologous, or Beg only qualify 
the term by refusing to regard them as strictly homologous. 
Again, the heemochyle or blood-lymph system of Vertebrates 
has no homogen, or but a very rudimentary one, in the other 
rade of animals. The vascular fluid of mollusks and insects 
as a homoplastic agreement with one part of the vertebrate 
the segmentation in various groups o _ the Annulosa, Leav- 
ing the question as to the origin of this i pores by 
ide, we are led 
. 
ancestor, the primitive Annelidan and Arthropodan sam 
two groups, and their points of contact 1n tegumentary deve- 
lopment, sense-organs, &c., are simply homoplastic, and not 
homogenous. 
may, it is suggested, be possibly solved by the 
admission of true zooid-segmentation as being frequently due 
to homoplasy, and not by any means necessarily an indication 
of genetic affinity. 
