INVEBTEBEATA, CllYPTOGAMIA, MICROSCOPY, ETC. 943 



p. Myriapoda. 



Segments of the Geophilidse.* — Dr. Sseliwanoff describes the 

 structure of the segmeuts iu these forms. 



Each body-segment, though bearing only a single pair of legs, is 

 clearly enough made up of two segments. In these the numerous 

 small lamelho which form the lateral jiarts, are arranged in two 

 transverse series. The number of these lamella) is greatest in the 

 lowest forms, while in those more highly developed the lamellae 

 either fuse with one another, or partially disappear. The same 

 remark applies to the distinctness of the two component segments 

 connected with each pair of appendages. The author is also reported 

 to have made some observations on Bothriogaster. 



7- Arachnida. 



Poison-organs of the Spiders.f — M. MacLeod, in this prelimi- 

 nary communication, deals chiefly with the histological characters of 

 these organs. Among the forms examined are Epeira diadema, Agelena 

 labyrhithica, and Tegcnaria domestica. 



In all these forms there are two j)oi son-glands, each of which presents 

 a pyriform glandular body, invested by a layer of spirally arranged 

 muscular fibres, and an excretory canal, which opens at the extremity 

 of the chelicorse. The gland is either jilaced in the cephalothorax, 

 immediately below the dorsal integument, or partly iu the cephalo- 

 thorax and partly in the basal joint of the cheliceras. Its wall is seen 

 to be composed, from without inwards, of the following layers : — 

 (a) a muscular tunic ; (h) a glandular epithelium. The former is 

 made up of a single layer of striated fibres, and is everywhere of the 

 same thickness. The transverse striation, though always distinctly 

 apparent, is but feebly marked. The longitudiiial strife are, on tho 

 other hand, very distinctly visible. Tho numerous nuclei are very 

 regularly arranged in longitudinal rows, and as many as four rows may 

 be made out iu a single fibre. On either side of the muscular layer 

 there is an investment of connective tissue, and they arc connected 

 together by regularly arranged septa, which traverse and scjiaratc 

 from one anf)ther the longitudinal constituents of tho muscular layer. 

 The elements of the glandular epithelium vary according to tho 

 ago and species of the specimen under examination. In a young 

 Agclcna they are cylindrical, with deeply set nuclei ; in the adult the 

 cells are more distinctly calyciform, and there is a narrow tube, three 

 or four times as long as tho protoplasmic portion of tho cell. 

 Numerous intermediate stages between tho extreme forms are to bo 

 noted. 



The excretory canal arises from tho narrowest part of the gland, 

 but the Inuscular tunic is formed of striated fibres, which are nrranged 

 s[)iriilly around the organ, and which are much more delicate and 

 more widely separated from one anotlier. The epithelial layer, which 

 invests tho inner face of tho internal layer of councctivo tissues, is 



♦ 'Zool. Anzi'ip;.,' iii. (1880) p. 1C7. 



t ' IJull. Acud R. Sci. Belg.,' 1. (1880) pp. llO-i:?. 



3 R 2 



