The Development of Theridium. 337 



fourth and fifth becoming the spinnerets. Lamellae appear on the 

 posterior surfaces of the appendages of the second segment before 

 these appendages invaginate. At reversion the fourth and fifth pairs 

 of limb buds have not begun to proliferate spinning glands. Each 

 pair of limb buds develops a pair of coelomic sacs, and so does the 

 caudal lobe, but in segments 6-8 such sacs do not become clearly 

 distinguishable 5 such sacs are in part occasioned by withdrawal of 

 mesoblast from the midline forming the ventral sulcus. At reversion 

 these sacs come to meet in the dorso-median line. 



With regard to the number of abdominal segTuents the authors 

 differ. Thus, anterior to the caudal lobe proper Claparede (1862) 

 found in PlioJcus eight segments and Schimkewitsch (1887) twelve; 

 Barrels (1878, Epeira) found nine; for Agelena Balfour (1880) 

 observed ''probably" nine, Locy (1886) "at least" ten, and Kishi- 

 nouye (1890, 1894) eight; Jaworowsky (1891) found twelve in 

 Trocliosa, and Pappenheim (1903) nine or ten in Dolomedes. Twelve 

 is the highest number given for any case and eight the lowest ; doubt- 

 less the number may differ in different species and be larger in the 

 more generalized, though the individual opinion of what constitutes 

 a segment probably introduces an error into the count. Barrois, 

 Balfour, Morin and Locy overlooked the first segment. Kishinouye 

 (1894) has given one of the most thorough accounts of the coelomic 

 sacs: ''The last three abdominal segments (sixth to eighth) gradu- 

 ally degenerate and .their coelomic cavities seem to fuse together into 

 one pair. The pair of coelomic cavities thus formed by fusion is 

 pushed into the protuberance of the tail as the jirocess of reversion 

 proceeds." Kishinouye found also that the first abdominal segment 

 disappears; and Bruce (1887) described "posterior to the last tho- 

 racic appendages a swelling. It corresponds in position to the oper- 

 culum of Limulus" ; judging from Bruce's figure, this is to be con- 

 sidered the first ganglion. Wallstabe (1908) found in Agelena nine 

 abdominal segments anterior to the tail lobe, with a pair of coelomic 

 sacs for each. 



Four pairs of abdominal appendages placed on segments two to 

 five inclusive were described by Salensky, Schimkewitsch, Kishin- 

 ouye, Wallstabe and Pappenheim, four pairs were seen also by Bar- 



