536 ANNULOSA, OR WORMS. 



kinds, first, a colorless fluid, containing numerous cell-like cor- 

 puscles, which can be seen in the smaller and more transparent 

 species to occupy the space that intervenes between the outer 

 surface of the alimentary canal and the inner wall of the body, 

 and to pass from this into canals which often ramify extensively 

 in the respiratory organs, but are never furnished with a return- 

 ing series of passages, and second, a fluid which is usually red, 

 contains few floating particles, and is enclosed in a system of 

 proper vessels, that communicates with a central propelling 

 organ, and not only carries the fluid away from this, but also 

 brings it back again. In Terebclla, we find a distinct provision 

 for the aeration of both fluids; for the first is transmitted to the 

 tendril-like tentacula which surround the mouth (Fig. 274, 6, 6), 

 whilst the second circulates through the beautiful arborescent bran- 

 chiae (&, k) situated just behind the head. The former are covered 

 with cilia, the action of which continually renews the stratum of 

 water in contact with them, whilst the latter are destitute of these 

 organs ; and this seems to be the general fact as to the several appen- 

 dages to which these two fluids are respectively sent for aeration, the 

 nature of their distribution varying greatly in the different mem- 

 bers of the class. The red fluid is commonly considered as blood, 

 and the tubes through which it circulates as bloodvessels ; but 

 the Author has elsewhere given his reasons 1 for coinciding in 

 the opinion of Mr. Huxley, that the colorless corpusculated fluid 

 which moves in the general cavity of the body and in its exten- 

 sions, is that which really represents the blood of other Articu- 

 lated Animals ; and that the system of vessels carrying the red 

 fluid is to be likened on the one hand to the " water-vascular 

 system" of the inferior Worms, and on the other to the trachea! 

 apparatus of Insects ( 391). 



363. In the observation of the beautiful spectacle presented by 

 the respiratory circulation of the various kinds of Annelids which 

 swarm on most of our shores, and in the examination of what is 

 going on in the interior of their bodies (where this is rendered 

 possible by their transparency), the Microscopist will find a most 

 fertile source of interesting occupation, and may easily, with care 

 and patience, make many valuable additions to our present stock 

 of knowledge on these points. There are many of these marine 

 Annelids, in which the appendages of various kinds put forth 

 from the sides of their bodies, furnish very beautiful microscopic 

 objects ; as do also the different forms of teeth, jaws, &c., with 

 which the mouth is commonly armed in the free or non-tubicolar 

 species, these being eminently carnivorous. The early history of 

 their development, too, is extremely curious ; for they come forth 

 from the egg in a condition very little more advanced than the 

 ciliated gemmules of polypes, consisting of a globular mass of 

 untransformed cells, certain parts of whose surface are covered 

 with cilia ; in a few hours, however, this embryonic mass elon- 



1 See his "Principles of Comparative Physiology," 4th E'fit. 218, 219, 292. 



