412 MR. J. B. GATENBY 0]S1 THE BIONOMICS, EMBRYOLOGY, 



vesicle glands of the bladder, and the Malpighian tubes take up the same 

 position as the enigmatic tubular glands do in the larva of Mic7'ogaster. The 

 gonad may or may not have altered its position : this is unimportant. 



Facts supporting my tentative conception of the homologies of the vesicle, 

 and vesicle glands of both kinds, in Microgaster, are as follows : — 



1. No proctodseum is demonstrable in the larva, v^^hile a distinct stomo- 

 dseum is present. 



2. In Braconid larvse (e. g. Apliidiiis) the number of Malpighian tubules 

 is two, the same number as the enigmatic tubular glands. 



3. It is hardly likely that the vesicle glands, which I consider excretory, 

 are new formations. It is far more likely that they are direct modifications 

 of some pre-existing organs (anal glands?). 



4. In the larva no chitinous papillse even of the finest description are to 

 be seen on the vesicle. All other true segments possess them. 



5. The bladder is not attached to the body in the same way that one true 

 segment is attached to another. Instead, there is a curious " bottle-stopper"' 

 joint. If it were a true segment there is no reason, to my mind, why there 

 should be a " bottle-stopper "" joint instead of the ordinary joint. A " bottle- 

 stopper " joint would automatically be produced by the invaginative process 

 conceived by me. 



6. Malpighian tubules are apparently, in insects, outgrowths of the 

 proctodseum {vide Seurat's p. 70, fig. 12 (12)). The tubular glands are 

 attached just at the correct region of the proctodseum if the vesicle be con- 

 sidered a proctodseum evaginated (see also MacBride's erudite work on 

 " Embryology,'" p. 260, for Malpighian tubes). 



Special attention is drawn to PL 26. fig. 25, v\'here the hinder region of 

 the gut is seen not to taper in any way. There is nothing that could be 

 interpreted as a proctodseal region in the shape of this gut. 



Several facts which will have to be explained before we can adopt my 

 present view with regard to the nature of the abdominal vesicle are as 

 follows : — 



1. There should be more segments than nine abdominals ; (but the " bottle- 

 stopper " joint might be formed of telescoped segments). 



2. The enigmatic tubular glands (Malpighian tubes ?) cojne to a point at 

 their distal end. Malpighian tubes never, to my knowledge, do this. 



3. If anal glands occur in Braconid larvae of the ordinary type, they are 

 either rare or have not so far been described. 



With regard to the last statement, it is equally true that such vesicle 

 glands (GL in PI. 24. fig. 6) had not before been described by anyone. 



The question as to the origin and true nature of the vesicle glands, 

 enigmatic tubular glands, and of the vesicle itself, will be settled by 

 examining early embryonic stages during the time the segments are appear- 

 ing, and at the time when the proctodseum is in other insects becoming 

 invaginated. Further work will be carried out on this iuieresting problem. 



