and Laboratory Methods. 1667 



well in salt or fresh water. It is hardy, well adapted for intra viiam stains and 

 for physiological experimentation. The chitin of the otocyst wall presents great 

 difficulties in technique. Freshly moulted specimens are more readily procured 

 from highly-fed young animals, and in these the chitin is easily sectioned. Large 

 antennules were decalcified in Gilson's fluid for 24 hours, or in Von Rath's 

 platinic-osmic mixture for a week or ten days. Best cytological results were 

 obtained with Von Rath's platinic-osmic-picro-acetic mixture followed by iron 

 haematoxylin. Fine differentiations of fibre tracts were obtained with Von Rath's 

 platinic chloride used for 3 to 5 days, followed by washing for two weeks in 

 90 percent, alcohol. For peripheral and central endings of nerve fibres methylen 

 blue was used as an intra vitam stain, injected in 1 per cent, solution in normal 

 NaCL Upon death of the animal the nerve tissue desired was dissected out 

 and upon reaching the proper degree of stain the tissue was fixed by Bethe's 

 ammonium-molybdate method. Tissues thus treated should not be long exposed 

 to xylol, as this extracts the stain. Preparations keep for about a year. 



The otocyst is located in the basal joint of the antennule in all decapod 

 Crustacea. Its chitinous lining is shed at each moult. The fringed otolith hairs 

 are borne upon one (^Macrnra) or three (^Brachyura) sensory regions, and are 

 attached by a thin walled basal bulb {Macrura) or in a cup-like depression 

 {Brachynra'), which affords freedom of movement. All sensory hairs are 

 formed by matrix cells beneath the hypodermis. When first found (after ecdysis) 

 processes from these cells extend into the shaft of the hair. In preparation for 

 the next moult these are withdrawn and the matrix cells recede from the base of 

 the old hair and arrange themselves around the nerve fibre for the formation of 

 the new bristle, which has the form, at that stage, of a double-walled tube, like 

 the withdrawn finger of a glove. The otoliths are grains of sand taken in from 

 the exterior and removed after each moult. In the absence of sand, iron filings 

 or organic matter may be placed in the otocyst. Tegumentary glands in the 

 wall of the otocyst secrete the cement which fastens the sand to the otocyst 

 hairs. The otocyst hairs are each innerveated by a single nerve element, which 

 terminates in the base without branching. The olfactory hairs, on the other hand, 

 receive fibres from 100 or more ganglion cells, which terminate free and at some 

 distance within the cavity of the hair. The central terminations of the sensory 

 fibres are at the posterior end of the brain, and are not directly connected with 

 ganglion cells. The author's results thus fall in line with the neurone theory. 

 The sensory ganglion cells are bipolar, and the nerve fibres possess a perifibrillar 

 matrix which forms the varicosities on the fibres with specific nerve stains. The 

 shrimp-like Decapoda have also a nucleated myelin sheath along the greater part 

 of the nerve fibre. The otocyst arises as an invagination of the dorsal ectoderm 

 of the basal segment of the antennule, becoming functional at the fourth moult. 

 Structurally the otocyst of the Decapoda may be roughly compared to the utriculus 

 of the vertebrate ear ; the sac of Palcetiionetes to a single isolated ampulla and 

 its sensory cushion to a crista acustica. The closed otocyst of Brachytira Avith 

 three sensory regions and no otoliths approaches more nearly the utriculus of 

 higher vertebrates. Experimental evidence is offered to prove that the otocyst 

 does not function as an auditory organ. It is rather an organ of equilibration, 

 sharing this function with the eyes and tactile bristles. In free-swimming 

 decapods it is the most important static organ. c. a. k. 



