59 



stage. The mouth parts are grouped nearer together and tend to 

 bend in over the opening of the stomodaeum. The two lobes repre- 

 senting the labium have grown together at their bases, making one 

 plate. The small knobs representing the antennae are still present, 

 but are very inconspicuous. The papilL-e representing the thoracic 

 legs and the abdominal appendages have now disappeared. 



The ganglia can be distinguished easily in faintly stained speci- 

 mens at this stage. There is a double chain of ten abdominal ganglia, 

 the last three of which are united in a compound ganglion in which 

 the three constituent ganglia are easily distinguishable by their 

 faintly-staining central portions. The double chain is continued in 

 the thorax as three separate pairs of ganglia, the anterior one of 

 which connects with the suboesophageal ganglion, which is easily 

 seen to be made up of three united pairs of ganglia. The sub- 

 oesophageal ganglion is connected with the supraoesophageal ganglion 

 by a pair of commissures as usual. 



Figure 25 represents an embryo at just about the time of hatch- 

 ing. It has practically the form of the young larva. The mesenteron 

 has the same form as in the preceding stage except that its anterior 

 end has narrowed considerably, giving it somewhat the appearance 

 of the neck of a bottle. This neck is open at the anterior end, and 

 encloses the posterior end of the stomodaeum which is now open 

 also, thus forming the valve-like connection between the stomodaeum 

 and the mesenteron. The proctodaeum has changed considerably in 

 shape. It has a middle portion which is wide and bladder-like, from 

 the posterior end of which a narrow tube-like part leads back to the 

 anus, and from the anterior end of which a short narrow part passes 

 forward to end blindly against the posterior end of the mesenteron, 

 the connection between these tw'o divisions of the alimentary canal 

 not yet having been formed. 



The mouth parts are practically the same as in the larva, and the 

 antennae have disappeared. The nerve' cord presents practically the 

 same appearance as in the preceding stage except that the last three 

 abdominal ganglia and the three parts of the suboesophageal ganglion 

 are more closely united. 



THE DEVELOPMENT OF T?IE EXTERNAL EORM OF THE EMBRYO OF 



Myrmica scabrinodis Nyl. 



Since a colony of Myrjjiica scabrinodis var. sabidcti which I had 

 in the laboratory was yielding an abundance of eggs while I was 

 w-aiting for my Caiiipo)iotus queen to begin laying, I decided to 



