1150 The American Naturaust. [December, 
follicle walls had applied themselves to the integument and to 
the intestine, and had adhered to them, these follicle-muscles 
could no longer function as such, and disappeared, except in the 
familiar longitudinal areas on the external body-wall, where they 
at first strengthened the primary longitudinal musculature, and 
later entirely supplanted it. 
Thus in the perfected organization of the Annelids we would 
look in vain for a primary longitudinal trunk musculature (per- 
haps excepting the Hirudinea); but, on the other hand, all the 
muscles arising from the embryonic mesenchym, as enumerated 
above, are to be regarded as handed down, with corresponding 
changes, from the parenchymatous ancestors. In this category 
belong the transverse muscles, so characteristic of the Annelids, 
and which are specially well developed in good swimmers. They 
may have moved from the intraseptal muscle region into the seg- 
mental cavity in a horizontal direction to increase the swimming 
movements, and have thus brought about a subdivision of the 
coelom into intestinal and nephridial or lateral chambers.’ 
From the parenchym also arises the retroperitoneal connective 
tissue, which, though occurring in Annelids in only small quantity, 
in some cases has a truly parenchymatous character, as cartilage- 
like supporting tissue. In addition, also, the blood corpuscles * in 
the blood vessels are a remnant of the primitive body-cavity. 
The excretory system of the Platyhelminths is commonly re- 
garded as belonging to the parenchym. Scarcely any one doubts 
that the larval nephridia of the Annelids are homologous to 
part of that system. I would also derive the definite nephridia, 
as has been variously done already, from these Turbellarian 
organs. In this I am guided chiefly by the occurrence of seg- 
mentally arranged primary nephridia in many larvae (two pairs 
in SS five pairs in Nereis and Dinophilus), as well as 
"Si appearances, the so-called protovertebrze of the Vertebrates correspond 
to the ee TORN of the Annelids, we would have to refer their ultimate origin to 
the mode of swimming in the Annelid ancestor, to the formation of these specific, trans- 
verse swimming mus: muscles, 
se) opposed to these proper blood corpuscles are the lymph corpuscles 
in the coelom, which, arising from the peritoneum, form, ertain extent, secondary 
leucocytes, » and are possibly related to the sexual products, somewhat as the cellular 
| products of the yolk glands in the Platyhelminths. 
