WITH THE MICROSCOPE. IO3 



Some observers think they have succeeded in injecting very minute 

 lymphatic vessels and demonstrating that these are continuous with 

 the capillaries. Such lymphatics are considered to ramify in the 

 intervals between epithelial cells. It is, however, doubtful if the facts 

 observed have been correctly interpreted. 



OF INJECTING THE LOWER ANIMALS. 



19O. insects. Injections of insects may be made by forcing the 

 injection into the general abdominal cavity, whence it passes into the 

 dorsal vessel and is afterwards distributed to the system. The 

 superfluous injection is then washed away, and such parts of the 

 body as may be required, removed for examination. Insects 

 should be injected very soon after they have emerged from the 

 pupa. 



The water vascular apparatus, the vessels, and the digestive 

 tube may be injected in many of the lower animals. In some cases 

 the best result? will be obtained with size coloured with transparent 

 colouring matter ; in others it will be found better to employ the 

 Prussian blue or carmine injecting fluid made with glycerine, 

 p. 95. In injecting the digestive apparatus of some entozoa as the 

 Iiver-fluke ; the pipe may be tied in, but as a general rule it is only 

 necessary to make an opening into the vessel and insert the pipe 

 which must be held steadily while the injection is carefully forced 

 from the orifice. In many fine injections a pipe of the form repre- 

 sented in pi. XXIII, fig. 157, with a blunt point and a lateral open- 

 ing will be found of great advantage. Coloured fluids will rise in the 

 vessels of most plants by capillary attraction, and occasionally the 

 vessels of some of the tissues of animals may be partially injected 

 in the same way. 



101. Moiiusca. (Slug, snail, oyster, &c.) The tenuity of the 

 vessels of many mollusca renders it undesirable to tie the pipe in them. 

 The capillaries are, however, usually very large, so that the injection 

 runs readily. In different parts of the bodies of these animals are 

 numerous lacunae or spaces, which communicate directly with the 

 vessels. If an opening be made through the integument of the 

 muscular foot of the snail, a pipe may be inserted, and thus the 

 vessels may be injected from these lacunae with comparative facility. 

 The large vessels of the branohise may be readily injected with the 

 aid of a pipe of the form represented in pi. XXIII, fig. 157. 



Milne Edwards injected the snail by passing the pipe through an 

 opening made with a sharp instrument at the base of the tentacle. 



