Proceplialic Lobes of Epeira Cinerea. 435 



figure appears to me doubtful, since no other investigators have 

 reported more than four pairs in all. In Epeira the first abdominal 

 segment is verj distinct, but never at any time does the trace of an 

 appendage appear upon it. 



It is possible that in some species of the Araneina the first 

 abdominal segment is not very clearly defined, and consequently 

 has been overlooked by those who have failed to report it as a limb- 

 less segment. On the other hand it may have been obliterated by 

 the strong tendency manifested by the most anterior of the abdomi- 

 nal segments to shift forward into the cephalo-thoracic region. 



The yolk, in this stage, bulges out between the lateral plates, and 

 is covered by a thin layer of ectoderm. The lateral plates are dis- 

 tinctly segmented, the segments extending to the dorsal margins of 

 the plates. The neuromeres which form the foundation of the nerve 

 cord are well foraied on the median margins of the plates. 



Several important changes have taken place in the cephalic plate. 

 The first of these is tlie formation of the semi-circular, or anterior, 

 groove {ant. gr.). This groove appears as a crescentic invagination 

 near the anterior margin of the head, and extends around the sides 

 to a point a little in front of the lateral gTOOves. Longitudinal sec- 

 tions show that the groove is formed by the infolding of the ecto- 

 derm in this region, shallow at first, but becoming gradually deeper 

 and deeper as the development of the embryo progresses. The lateral 

 grooves, at the same time, have deepened considerably and form 

 conspicuous pits on the lateral margins of the head (lat. gr.). 



Each lobe of the pre-cheliceral portion of the cephalic plate con- 

 sists of three segments, the first lying in the region of the anterior 

 groove, not far from the margin of the head, the third being in close 

 proximity to the cheliceral segment (cgP and cJil. seg.). In some 

 instances, in embryos of this stage, the cheliceral and third cephalic 

 segments lie directly against one another. 



The thickened portions of each of these segments lying toward the 

 median line (c. gl.) forms a neuromere-like structure which, as has 

 already been pointed out, forms the foundation of a cerebral ganglion. 

 The series of cerebral" ganglia, in each lobe of the cephalic plate, is 

 continuous with the chain of neuromeres of the thoracic and abdom- 



