Structure and Growth in Animals and Plants. ^7 



The fatty cells of the cellular tissue of the foetus have likewise at first 

 a very distinct cellular nucleus. If the mcmbrame of the cell be thin, the 

 nucleus rises above the drop of fat which encloses this membrane, a cir- 

 jpumstanee which docs not take place when it is thick. The nucleus con* 

 tains one or two nucleolules. The fatty cells of the skull of young Red- 

 eyes {Cyprinua erythrophthalmus, L.) have sometimes two nuclei dis- 

 posed in the same manner relatively to the membrane of the cell. There 

 «till exists in the cellular tissue of the foetus a third species of cells ; they 

 are round and pale, containing a nucleus at their wall, with one or two 

 nucleolules, not prolonged into fibres, and enclosing no fatty matter, 

 but filled with small grains ; this granular precipitate first shews itself in 

 the vicinity of the nucleus. The cellular tissue of the foetus yields no 

 gelatine by boiling ; the decoction contains a substance like pyine, with 

 this difference, that the muddy precipitate, produced by hydrochloric 

 acid, in the case of the latter, disappears by an excess of that acid. 



2, Tissue of tendons. — The tendinous fibres derive their cells in the 

 same manner as the fibres from the cellular tissue. 



3. Elastic tissue. — The medial tunic of the arteries of the embryos of 

 swine, 6" long, contains many insulated cells, some of them round, others 

 terminated by two or three prolongations, which are again divided. On 

 the inner side we perceive the ordinary nucleus of the cell, with one or 

 two smaller nuclei ; we find, besides, an elastic tissue already formed. 

 The ramified fibres of the elastic tissue, which are hollow, according to 

 Purkinje, appear to come from their cells. 



Fifth Class. — The following is the type of formation in this class : 

 first, there exist rounded or cylindrical cells, or else these are stelliform. 

 In the former case, the primitive cells are placed one after another, and 

 soldered to each other at their point of contact. The partitions are then 

 absorbed, so that the primitive cells are changed into secondary ones. 

 The latter increase like simple cells. Such appears to be the mode of 

 formation of the muscles and nerves. 



In the second case, the stelliform cells meet at their prolongations 

 where they unite ; the walls are absorbed, whence a net-work of canals 

 results. 



1. Muscles. — According to Valentin's observations, the primitive mus- 

 cular bundles are formed of small grains, placed one behind another, and 

 soldered together; the primitive fibres only come from the division of 

 the fascicle into smaller fibres- Schwann has observed in the cylinders 

 of the primitive fascicles of a pig's foetus, about 3i" in length, a deeper 

 border and an internal part, no doubt the cavity. In the clearest portion 

 he could distinguish, besides some small granules, corpuscles of a larger 

 size, oval and flattened ; these nuclei often enclosed one or two other 

 smaller nuclei. They are placed at more or less regular distances from 

 each other, in the thickness of the cylinder and against its wall. In mus- 

 cles of greater age, no trace of cavity could be seen, but the nuclei still re- 

 mained a long while visible, and are situated in the thickness of the fibre, 



