EMBRYOLOGY 63 



3. The opening of the generative organs being in the front 



part of the body. 

 It differs from Chilognatha in the following respects : — 



1. The legs are not of equal length,, the posterior legs 



being the longest, as in Chilopods. 

 '2. The mouth parts differ from those of Chilognaths 



almost as much as from those of Chilopods. 

 3. The form of the antennae. 

 Only a few Pauropoda have been discovered as yet. 



Embryology. 



The preceding account of the anatomy of ilyriapods would be 

 incomplete without some reference to the wonderful manner in 

 which the different organs of the body are built up ; the whole 

 of the complex organism proceeding by a gradual and regulated 

 process of development from a simple cell called the ovum derived 

 from the female body, and united with a cell from the male body 

 (called the spermatozoon). I hope to be able to give my readers 

 some idea of the interest which the pursuit of the difficult study 

 of embryology adds to anatomy, by offering us a key to the inter- 

 pretation of the relations between our knowledge of the forms at 

 present living on the earth and those which, we learn from 

 Palaeontology, have inhabited our planet in past ages. 



Like all living creatures with which we are acquainted, the 

 starting-point of Myriapod life is the ovum, 

 as it is called. This ovtt7n is a cell resem- 

 bling the cells of which the body of all f^^^vJI^srV""''^' 

 living animals are built up, and which 

 may be compared to the bricks of which 

 a building is composed. This cell or 

 ovum is a small sphere of living trans- „ „„ ,, 



-., , , 1 J -i. I^IS. 36. — Young ovum of 



parent substance called protoplasm, and it j^i^ terrestris: mid, 

 is nucleated — that is, it contains a small nucleolus; ««, nucleus; 



R, first appearance 01 



spot of denser protoplasm called the yoik ; f, follicle cells. 

 nucleus, and within that a still smaller 



spot of still more dense protoplasm called the nucleolus. In the 

 process of impregnation the ovum unites with the male cell, and 

 the cell so formed is called the impregnated ovum. This ovum 

 has the property of dividing into two cells, each resembling the 



