272 



AYERS ON THE DEVELOPMENT 



vous cord, but are connected to the blind end of the mesenteron by protoplasmic 

 filaments, usually one to each mother cell. The invagination of the proctodaeum, the 

 walls of which are intimately connected with this mass, was not very satisfactorily made 

 out, since its lumen can only rarely be observed (pi. 25, fig. 13), and never with the 

 distinctness shown in Ganin's figures of Platygaster. The size of the nerve cord con- 

 necting the posterior enlargement with the suboesophageal ganglion varies much in 

 different individuals, the abdominal portion being sometimes of the same diameter as 

 the latter. The cells forming the cortical layer of the abdominal enlargement possess 

 the same characters as the cells of the corresponding layer of the brain mass. The poste- 

 rior enlargement is usually lobed ; bi- and trilobed forms being of most frequent occurrence. 

 Nothing that could be interpreted as peripheral nerve fibres has as yet been differentiated, 

 but the protoplasmic filaments which throughout the body are stretched between the 

 mesenteron and body wall may possibly serve to transmit the nervous impulses to the 

 muscles and to the cells of the enteric tract. No nuclei could be distinguished in these 

 protoplasmic filaments, so common throughout the body, and their contractile nature 

 was not determined with certainty. 



This stage closes the history of the development of the parasite up to date (April 1st). I 

 have not as yet observed the ovate, flattened form which succeeds the cyclops stage in the 

 development of other species of the Pteromalidae, but specimens which were apparently 

 approaching this stage were found in two instances. This was indicated by their greater flat- 

 ness and the proportionate increase in the size of the abdominal over that of the head region. 

 The abdominal region in this stage exhibits no traces of division into segments. The number 

 of ecdyses is unknown. There are at least four, but how many more there may be it is 

 impossible to state. 



Explanation of the Plates. 



The following letters are used consistently in explaining the figures of Oecanthus and Teleas. 



A. 



B. 



