206 THE MICROSCOPIST. 



quired to show the formative layers. In the later stages 

 dissection is required, and is best performed with embryo 

 preserved in spirit. If living embryos are placed in spirit, 

 a natural injection of the vessels may be obtained. 



III. OKGAKS OF THE BODY. 



Anatomists usually group the organs into systems, as 

 the osseous, muscular, nervous, vascular systems, etc., but 

 for histological study a classification based on physiologi- 

 cal considerations may be more convenient for the student. 



I. VEGETATIVE ORGANS. 



1. Nutritive, or organs pertaining to the absorption and 

 distribution of pabulum, including the digestive and cir- 

 culatory organs. 



The mucous membrane of the intestinal canal contains 

 many follicles and glands, whose secretions serve impor- 

 tant offices in the preparation of the food. These will be 

 referred to in the next section. The epithelium of the 

 intestinal canal is columnar, except in the oesophagus, 

 where it is laminated. Beneath the glandular layer of 

 the stomach is a stratum of fibrous connective tissue and 

 muscle fibres in two layers, an internal with transverse, 

 and an external with longitudinal fibres. The tissue of 

 the small intestine beneath the epithelium is reticular 

 connective, entangling lymphoid cells. The structure of 

 the large intestine is similar to that of the stomach. The 

 villi of the small intestine begins at the pylorus, flat and 

 low at first, but becoming conical, and finally finger-like 

 in shape. The epithelium of the villi are columnar, with 

 a thickened and perforated edge (Plate XXII, Fig. 161). 

 Between the epithelial cells of the villi, peculiar "goblet- 

 cells" are often found, which Frey supposes to be decay- 

 ing cells. The reticular connective tissue of each villus 

 is traversed by a vascular network, a lymphatic canal or 

 lacteal, and delicate longitudinal muscular fibres. If the 



