Germ Cells of Leptinotarsa SignaticoUis. 145 



a limiting membrane, he believed the terminal thread served as a 

 ligamental structm-e. Kramer ('69) regarded the thread as the 

 solid continuation of the tunica propria of the egg tube. 



As a matter of fact an almost unlimited variety of functions, 

 from that of a blood vessel to that of a piece of connective tissue, 

 have been ascribed to the terminal portion of the ovariole. This 

 is largely because most workers have confined their studies to the 

 adult organ which represents the end-product of a developmental 

 process. Furthermore, this structure does not present the same 

 appearance in all species, and all gradations are to be found from 

 a condition where it is a mere rudimentary appendage of the egg 

 tube, to cases where it is a direct continuation of the terminal 

 chamber. Agreement as to its significance can scarcely be expected 

 as long as observations are based almost entirely upon the adult 

 structure. 



Heymons ('91) was perhaps the first to study the development 

 of the terminal thread, and he showed in B. germanica that its 

 cells, as well as the epithelial cells, are derived from the dorsal 

 wall of the primitive mesoblastic somite. According to this 

 author the terminal thread does not contribute epithelial cells to 

 the terminal chamber. In the adult he found the thread ending 

 freely, so that if a supporting function is to be attributed to any 

 part of the apparatus it is concerned with the peritoneal sheath, 

 and not with the cells filling the interior. However, he considers 

 this of no great importance, since the fat-bodies, connective tissue, 

 and tracheal tubes serve to hold the organs in place. The end 

 threads are of functional significance only in embryonic and larval 

 periods of development, when they are concerned with orienta- 

 tion of the ovarioles which, as I understand him, consists in 

 directing the growth of the egg tubes backward and upward 

 toward the dorsal wall of the primitive segments. 



The appearance of the terminal thread in the adult of L. sig- 

 naticollis would justify the conclusion that it is a rudimentary 

 appendage of the terminal thread from which it is separated by a 

 definite membrane (Fig. 13 I. m.). The peritoneal sheath has 

 become invested with striated muscular tissue and air tracheae, 

 which form a thick covering grading off into the region of the egg 



