108 ESSENTIALS OF ZOOLOGY 



cornea focussed, it will be found that a very sharp image of 

 a moving object, such as a pencil held in the hand, can be 

 obtained by lowering the microscope tube so as to bring the 

 rhabdomes into focus. 1 



The auditory organ in the basal segment of the antennule 

 is a sac-like ingrowth of the integument, containing a watery 

 fluid, and furnished with setae and small concretions. The 

 setae are connected with the antennule nerve, and appear to 

 be the means of transmttiing vibrations to the brain. The 

 organ also is associated with co-ordinating movements, with 

 the sense of position, and maybe also with the homing in'stinct. 

 The antennules perform what in the water answers to the 

 olfactory function. 



Excretory Organs. The green gland, or antennary gland, 

 is a coelomiduct. It consists of an end sac, the reduced coelom, 

 a plexus of tubules forming the glandular portion, a wide bladder 

 and a ureter, the latter ending in the pore on the basal segment 

 of the antenna (fig. 49, C). The glandular part has an alkaline 

 reaction, and the green colour is due to the guanin which with 

 uric acid has been shown to form part, at least, of its excretory 

 products. Excretion appears also to be shared by the groups 

 of cells found in the gills (branchial glands) and by the liver. 

 The cuticle shed at ecdysis may also be recorded as an excre- 

 tion. The branchial glands are probably environment organs 

 (p. 130). 



Reproductive Organs. Male. The testes consist of two long, 

 straggling, irregular-folded lobes, extending from the stomach 

 to the beginning of the second abdominal segment. They 

 are joined together just beneath the heart, and from that 

 region the vasa deferentia pass out as slightly coiled tubes 

 to open in each case on the basal element of the last pereiopod. 

 Each vas deferens is made up of a short, narrow, coiled portion, 

 a dilated glandular middle part, and a muscular region. The 

 spermatozoa have a rather remarkable appearance. They 

 consist of a nucleated central portion produced into one long, 

 usually straight, process, homologous with the flagellum of the 

 flagellate sperm, and three smaller curved processes derived 

 from the neck ; that is to say, between the flagellum and the 



1 1910. Demoll, Ergeb. und Fortschritte der Zoologie, Bd. 2. 



