674 NOTES ON THE DEVELOPMENT OF THE ARANEINA. 



be the same as the dorsal organ of the embryo before the form- 

 ation of any segments, especially as all the stages between the 

 two appear to have escaped him. In Agelena there is undoubt- 

 edly no organ in the position he gives when six segments are 

 found. 



Balbiani's observations accord fairly with my own up to the 

 stage represented in fig. 2. Beyond this stage my own observa- 

 tions are not satisfactory, but I must state that I feel doubtful 

 whether Balbiani is correct in his description of the gradual 

 separation of the procephalic lobe and the cumulus, and the 

 passage of the latter to the dorsal surface, and think it possible 

 that he may have made a mistake as to which side of the pro- 

 cephalic lobe, in relation to the parts of the embryo, the cumulus 

 is placed. 



Although there appear to be grounds for doubting whether 

 either Balbiani and Claparede are correct in the position they 

 assign to the cumulus, my observations scarcely warrant me in 

 being very definite in my statements on this head, but, as already 

 mentioned, I am inclined to place the organ near the posterior 

 end (and therefore, as will be afterwards shewn, in a somewhat 

 dorsal situation) of the ventral embryonic thickening. 



In my earliest stage of the third period there is present, as 

 has already been stated, a procephalic lobe, and an indistinct 

 and not very prominent caudal portion, and about three segments 

 between the two. The definition of the parts of the blastoderm 

 at this stage is still very imperfect, but from subsequent stages it 

 appears to me probable that the first of the three segments is 

 that of the first pair of ambulatory limbs, and that the segments 

 of the chelicerae and pedipalpi are formed later than those of 

 the first three ambulatory appendages. 



Balbiani believes that the segment of the chelicerae is formed 

 later than that of the six succeeding segments. He further 

 concludes, from the fact that this segment is cut off from the 

 procephalic portion in front, that it is really part of the pro- 

 cephalic lobe. I cannot accept the validity of this argument ; 

 though I am glad to find myself in, at any rate, partial harmony 

 with the distinguished French embryologist as to the facts. 

 Balbiani denies for this stage the existence of a caudal lobe. 

 There is certainly, as is very well shewn in my longitudinal 



