Echinoderma. 



cells, derived from the genital tube. These swellings increase in size and com- 

 plexity and become ovaries or testes. The dorsal schizocoel ring of a young Ur- 

 chin contains a genital tube filled with germ-cells , outgrowths from which deve- 

 lop into ovaries or testes. Similar amoeboid cells occur in the immature genital 

 organs of Holothurians. 



Kbhler compares his own observations on the Ophiurids with the results 

 gained by other workers in the remaining groups of Echmoderins. The vascular 

 system has the same lacunar structure in Ophiurids and Asterids , but in neither 

 group does the madreporic gland or dorsal organ communicate with the exterior 

 through the rnadreporite [see Bericht for 1886 Ech. p 3]; while the dorsal 

 schizocoel spaces of the Asterids and the so called vascular structures which they 

 enclose are absent in Ophiurids [see Hamann, infra, p 8]. On the other hand the 

 madreporic gland of the Urchins communicates with the exterior [see infra, pp 10, 

 13, 14 and Bericht for 1886 Ech. p 1 1] and there are intestinal vessels, true ca- 

 nals with a perfectly free lumen ; but the radial portions of the vascular system 

 are not lodged in perihaemal spaces, being outside the perineural canals. The cir- 

 culatory system of the Crinoids, as described by Perrier and by Vogt & Yung, is 

 very different from that of other Echmoderms [see Bericht for 1886 Ech. p5, 6]. 



Perrier points out how the observations of Prouho ( J ) and Cuenot (') respecting 

 the relations of the genital organs to the ovoid gland of Urchins and Asterids 

 agree with those previously described by himself [see Bericht for 1886 Ech. 

 p 5, 9]. 



Semon ( l ) finds that the fundamental form of the calcareous spicules (of the 

 Echinid Pluteus) has 4 axes and not 3 only, as described by Selenka ; but after 

 the spicule has reached a certain size within its formative cell , further develop- 

 ment takes place along 3 axes only , the necessary material being furnished by 

 calcareous granules contained in adjacent cells. Each spicule is surrounded by a 

 thin homogeneous envelope and its central canal is occupied by an organic axis- 

 substance. Around this are alternating layers of calcareous and organic substance, 

 the latter being very thin and connected to one another by delicate radiating 

 fibres. The fundamental form of all the calcareous deposits of Echinoderms, both 

 larval and adult, is also tetrahedral ; but in the wheels of Holothurians and in the 

 spines of the Echinozoa development takes place along all 4 axes , and not along 

 3 only as in the Pluteus larvae. The thicker limestone plates are formed by re- 

 peated division of the spicules at an angle of 120, so that the meshes of the 

 network are at first regular hexagons , though they afterwards become more cir- 

 cular. 



Preyer has continued his investigations into the functionsof the nervous system 

 in Starfishes and extended them to Crinoids. Comatula responds very readily to all 

 forms of stimulation. If it is weak only the stimulated arm is affected, but a stron- 

 ger or more prolonged stimulation causes more arms to take part in the movement, 

 though very slight injuries will prevent irradiation of the stimulus. When a living C. 

 is put into fresh water a short period of inactivity is followed by vigorous move- 

 ments of all the arms , which is succeeded by almost complete quiet ; while the 

 colouring matter is mostly discharged into the water. Stimulation of a Starfish is 

 not so constantly followed by its retreat along a straight line as stated by Kornanes 

 & Ewart [see Bericht for 1882 I p 177J, this being only one of many possible 

 movements. Some Asterids and Ophiurids, when put into abnormal positions, will 

 return to them again after more or less successful attempts to leave them. The 

 most remarkable instances of this are retreat into narrow necked bottles to avoid 

 exposure to the air , which is only brought about by unwonted contortions of the 

 body, and to a certain extent also by a diminution of volume owing to the empty- 



