ON THE DEVELOPMENT OF ARANEINA. 73 



and infrfi-œsophageal ganglia. They are in contact with each other 

 at the anterior part. The basal joint of the pedipalpi is very broad, 

 the maxillary part being- easily distinguished. The ganglia of the 

 pedipalpi and of the succeeding four thoracic segments are well deve- 

 loped and are in close contact with each other, thus forming the 

 large snb-œsophageal ganglion. The ganglia belonging to the abdo- 

 minal segments are also well developed. . : 



The stomodœum elongates itself obliquely upwards and is sur- 

 rounded externally by the well developed upper and lower lips (PI. 

 XIII, figs. 19-21 ; PI. XIV, figs. 24-26). The ectoderm forming 

 the wall of the stomodieal invagination is thick. 



The ectoderm of the ventral part of the anal lobe is conspicuous- 

 ly thicker than that of the dorsal part, being continuous with the 

 two ventral l3ands. At the beginning of the reversion, it is 

 uniformly two or three cells deep (PL XIV, fig. 27); but when 

 the reversion is fairlv advanced, so that the elono-ated anal lobe beo'ins 

 to become short again, the cells in the middle part of it are elongated 

 and thei'e they are only one cell deep (fig. 28). At this part an in- 

 vagination takes place (fig. 29). Fnjm this stage the ectoderm of 

 the ventruni of the anal lobe, placed anterior to the invagination be- 

 comes two or three times thicker than the posterior part, and is dif- 

 ferentiated to form the anal ganglia (figs. 29-32, (r). The invagination 

 is the protodaeum. It is very shallow and small, aud its bottom is 

 in direct C(3ntact with the wall of the stercoral pocket. The wall of 

 the prootodasimi is thinner than that of the stomodsenm. It is 

 remarkable that the proctodîeum is not formed at the extreme hind 

 end of the ventral plate but somewhat in front of it directly behind 

 the- anal- ganglia, and that both the stomodœum and the proctodaemn 

 are produced at the two extremities of the nervous system simulta- 

 neously with the development of the latter near them. The portion 



