GENEKATION OF INSECTS. 389 



tlic generative organs of the male are, however, in the Chilognatha, 

 as in many Crustacea, situated on a segment posterior to that which 

 is perforated by the generative organs in the female. 



In the male Gally-worm (lulus terrestris), the testis consists of 

 minute ca3ca appended, for the most part alternately, to the sides of a 

 long efferent tube : there are two of these on each side, which, com- 

 mencing in the posterior fourth of the body, advance forwards, and 

 unite on each side so as to form a pair of tubes ; the ciecal glands 

 continue to be developed, but in smaller number, and from one side 

 principally of each of the common tubes. These tubes then ap- 

 proximate, communicate together by three or more transverse canals, 

 and, after a slight bend or convolution, extend straight forward to 

 the sternal arc of the seventh segment of the trunk, where they ter- 

 minate by distinct orifices, on short conical pi'otuberances, behind the 

 seventh pair of legs. 



The structure of the spermatic 'coeca is so similar to that of the 

 longitudinal tubes, tliat the secerning function is doubtless exer- 

 cised by both parts ; they consist of a thick mucous coat, with an 

 external muscular tunic ; they are situated beneath, or ventrad of, 

 the alimentary canal, and between the two large salivary vessels. 

 In the Crustacea the testes are dorsad of the alimentary canal, and 

 their ducts external to the glandular appendages of that canal. 



The transverse anastomosing canals, between the right and left 

 testes, remind one of the single transverse communication between 

 the two testes in the lobster and in the crawfish ; but this character 

 is so multiplied — Newport * having found more than twenty such 

 transverse canals in one species of lulus — that the testes oifer no 

 unapt resemblance to a ladder. In a large species the same la- 

 borious entomotomist discovered that the semicorneous intromittent 

 organ was defended by an uncinated valve, serving as a holder or 

 clasper. 



The contents of the testes are a clear fluid at the hinder beginning 

 of the organs, but it becomes thick and more opaque as the outlets 

 are approached. The change is due to the appearance of numerous 

 sperm cells, l*450thof aline in diameter, with a highly refracting 

 nucleus l'750th of a line in diametei', lying close to the cell- wall. In 

 the progress of development the nucleus enlarges and becomes conical, 

 the apex protruding from the surface of the cell, which finally dis- 

 solves and leaves the nucleus free. This is the spermatozoon : its 

 breadth always exceeds its height or length. In the lulus fab ulos us 

 the cell-wall becomes enlarged at the part opposite to the nucleus, 



* ecu. p. 101. 

 c c 3 



