SUBFAMILY DIASPIDINAE 225 



To Berlese belongs the credit for determining and describ- 

 ing the structure of the cells forming the threads of wax in the 

 Diaspidinae. These cells are modified hypodermal cells but are 

 very different from the flask-shaped cells connected with the 

 spiracerores and genacerores which excrete powdery or pulveru- 

 lent wax. The thread excreting cells are long and club-shaped, 

 each connected with the ental surface of the ental or free trun- 

 cated end of a ceratuba. Each ceratuba bears a group of three 

 cells, known as a diaspicera, one of which is supposed to excrete 

 the wax and the other two a covering for the wax. The wax cell, 

 the silk gland or ghiandola sericipara of Berlese, is attached to 

 the end of the bulla. The other cells, the ganogene cells, the 

 ghiandole ganogene of Berlese, are also attached, one on each side 

 of the wax cell, to the bulla. There are openings in the bulla 

 through which the excretion of these cells is poured. The struc- 

 ture of the wax cell is anomalous, according to the account and 

 figures of Berlese they are more like a multicellular gland in 

 structure than a single cell. The distal portion of this cell or 

 the secreting portion is flask-shaped and contains a single large 

 nucleus. The secreting portion is connected by a greatly elon- 

 gated neck-like or tubular portion through which the excretion is 

 passed to the bulla and ceratuba. The tubular portion of the 

 cell adjacent to the bulla is thickened and striated and apparent- 

 ly functions for compressing the thread of wax in somewhat the 

 same way that the press of the silk duct in lepidopterous larvae 

 compresses the two components of each thread. The ganogene 

 cells are about one-fourth the length of the wax cell. Each con- 

 sists of a distal, club-shaped, excreting portion which contains a 

 single nucleus. There is a short tubular portion connecting the 

 excreting portion with its opening in the bulla. Berlese believed 

 that the function of the ganogene cells was to excrete a substance 

 which was used for coating or covering the exterior of the threads 

 of wax. If this suggestion is correct, the threads must be fully 

 formed when they make their exit from the bulla into the cera- 

 tuba and this latter structure can serve only as a reservoir for 

 storing the threads. The attachment of the cells to the ental 

 surface of the ceratuba would suggest that the bulla and associ- 

 ated parts might be a ceroris that had been invaginated. These 

 structures were figured by Childs, but no discussion of his con- 

 elusions is given. 



