252 ANIMAL BIOLOGY. [Part II. 



3. The crystalline cones are dioptric, the connective rods and 

 the striated spindles being the true end organs continuous with 

 the nerve-fibrils. 



The third answer is that most generally accepted. On this 

 view the spindles, nerve-fibrils, and ganglion-cells answer to the 

 vertebrate retina. Note that, if this be so, in the arthropod the 

 recipient end-organs are turned towards the source of light, and 

 not away from it as in the vertebrate. 



Organs of Reproduction. (L) In the Hale. The spermary, or 

 testis, has two anterior lateral lobes and one median posterior 

 lobe. Its position is seen in Fig. 75, a. t., p. t. From the points 

 where the anterior lobes join the median lobe there arise the 

 much-coiled vasa defer entia, which, after a convoluted course, 

 pass downwards to open on the basal joints of the last thoracic 

 appendages. 



In minute structure the testis shows an immense number of 

 vesicles attached to the ducts which lead to the vasa deferentia. 

 These acini are aggregated into lobules. The large nucleated 

 cells which line the cavities of the acini multiply rapidly with 

 karyokinesis (p. 89), and are eventually converted into sperma- 

 tozoa of the peculiar and unusual form shown highly magnified 

 in Fig. 79, A. In the vasa deferentia they become invested 

 with a viscid secretion. The vermicelli-like matter thus pro- 

 duced is deposited by the male on the posterior thoracic and 

 anterior abdominal somites of the female. 



(2.) In the Female. The ovary is in shape somewhat like a 

 shortened thickened testis. The short wide oviducts pass down- 

 wards from its ventral side to open on the basal joint of the 

 second leg (sixth thoracic appendage). Note, as something 

 different from what we have seen in the frog, fowl, or rabbit, 

 that the lumen of the oviduct communicates with the hollow 

 interior of the ovary. The development of the ova may be 

 thus summarised. 



1. A group of cells forms a papilla projecting into the cavity, 

 and covered by a structureless membrane, the membrana propria 

 (m. pr.) Such a group forms an ovisac. 



