530 SUMMARY OF CURRENT RESEARCHES RELATING TO 



lining of the otocyst-sac bears in Macrura a single sensory prominence,, 

 and in Brachyura three sensory regions. The hairs borne on these 

 regions are heavily fringed and often bent or hooked. In Macrura they 

 are attached to the wall of the sac by a thin bulb of chitin ; in Brachy- 

 ura the base of the hair-shaft is inserted into a cup-like depression. In 

 addition to these otolith hairs, there are in the lobster and in Brachyura 

 very long and delicate free hairs (thread-hairs). The otoliths are re- 

 newed after each moult ; they may be free or attached to the sensory 

 hairs. They are absent in the Brachyura except in the megalopa stage. 

 Where they are attached to the hairs, glands, similar to the tegumentary 

 glands, are present beneath the sensory cushions which bear the hairs. 

 In decapods with free-swimming larval stages, the otocyst develops as 

 an invagination of the dorsal ectoderm of the basal segment of the 

 antennule, and becomes functional only at the fourth moult after hatching. 

 The matrix cells from which the sensory hairs are to arise appear in the 

 first larva ; invagination begins at the second larval stage ; in the third 

 the hairs appear below the floor of the shallow sac ; while at the fourth 

 they become functional, and the otoliths appear. The zoea of the cr;ib 

 has no functional otocyst. In the megalopa it is open and contains 

 otoliths and hairs ; later it loses the otoliths and becomes closed. 

 Structurally, the otocysts of decapods may be compared to the utriculus 

 of a Vertebrate like Myxine, the sensory cushion of Palseomonetes re- 

 calling the crista acustica, while the more elaborate otocyst of the crab 

 approaches in general structure the utriculus of the higher Vertebrates. 

 There is no evidence that the otocyst has anything to do with audition, 

 but much to show that, together with the eyes and the tactile bristles, it 

 functions as an equilibrating organ. In free-swimmiug decapods the 

 otocyst is by far the most important of these static organs, its removal 

 resulting in a great loss of the power of orientation. In adult Brachy- 

 ura the otolith-hairs have become practically functionless, but the 

 slender free hairs are so modified as to respond directly to the attraction 

 of gravity. 



Pacific Crustacea. * — Prof. H. Lenz describes the Crustacea of 

 Schauinsland's expedition. The collections included ninety-nine species,, 

 of which three are new — a species of Hippolyle, one of Eupagurus, and 

 one of Pinnotheres. 



Eyes of Entomostraca."j" — J. Kunstler aud Ch. Gineste find that in 

 certain of the lower Crustacea there is a distiuct articulation between the 

 crystalline cone and the rhabdom. The rhabdom is a cellular product 

 of a mother-cell, just as the crystalline cone is a product of a crystalline 

 cell. The rhabdom mother-cells cannot be regarded as retinal cells in 

 the ordinary sense, for they form with the rhabdom an indivisible uni- 

 nucleated whole. Further details and figures are promised. 



Structure of Amoeboid Corpuscles in Crustacea.J — J. Kunstler and 

 Ch. Gineste find that the lacunas of the general parenchyma in certain 

 of the lower Crustacea contain corpuscles of remarkable structure, which 

 tend to show that protoplasm is not quite so simple as some modern 

 investigations would suggest. Both cytoplasm and nucleus have a 



* Zool. Jahrk, xiv. (1900) pp. 429-82 (1 pi.). 



t Proc. Verb. Linn. iSoc. Bordeaux, 1901, 7 pp. J Tom. cir., 3 pp. and 4 figs. 



