ZOOLOGY AND BOTANY^ MICROSCOPY, ETC. 347 



Diadema setosum and D. mexicanum ; these, wliicla are about 2 mm. 

 long, are elub-s]iaj)ed and end in a very short and delicate pedicle ; 

 they enclose three large elongated glands with an orifice at their 

 upper end ; the glands are closely applied to one another, but have 

 superiorly, where they diminish in size, six separating cavities which 

 may be looked on as the homologue of the head of the pedicellariee of 

 S. granulans. In Mespilia globulus the pedicellariae are excessively 

 small and very numerous. In Strongylocentrotus lividus and S. dro- 

 bachiensis the gemmiform pedicellariae have a stalk which has consi- 

 derable resemblance to that of the ophiocephalous and tridactyle 

 pedicellarige. When we compare S. granulans with Echinometra and 

 Diadema we find that in the first the glands and head are equally 

 developed, that in the second the glands are rudimentary, and that 

 in the third it is the head which is rudimentary. 



The author, not having been able to make any original observa- 

 tions on living forms, accepts the views of Sladen, who was the first 

 to direct pointed attention to this subject. 



Circulating Apparatus of Starfishes.* — E.Perrierand J. Poirier, 

 after noticing the accounts of earlier observers, in which there is a 

 large amount of very perplexing contradiction, state that they find 

 that the vascular apparatus described by Ludwig in the partition of 

 the infrabrachial canals has no existence, that the partition is not 

 continuous, but that it is reduced at certain points to a vertical 

 lamella while at others it presents distinct foramina. The body 

 adherent to the hydrophoral canal, where Ludwig sees a plexus of 

 vessels and which he regards as being the heart, is (as Jourdain 

 showed in 1867) nothing but a gland ; the same has been shown to be 

 the case in the common sea-urchin, and Koehler has found the same 

 to be true for the Spatangidae. As the Ophiuroidea present a similar 

 structure, we may say that, in all Echinoderms, this so-called heart 

 is a simple gland. 



The system of lateral branches described by Hoffmann as arising 

 from the infrabrachial canals, has been detected, but a different 

 account is given of its relations. These lateral branches do not 

 curve round the ambulacral pore, but pass straight to the edge of the 

 ambulacral groove ; what Hoffmann took for the second branch of 

 the horse-shoe is a fresh canal, independent of and identical with 

 the first ; and these two canals pass, parallel to one another, to 

 the edge of the arm ; there they bifurcate and the two neighbouring 

 branches together pass through a foramen between two contiguous 

 ambulacral, and the adjacent adambulacral pieces. In these foramina 

 the two branches unite to form a common branch, which opens 

 directly into the general cavity. There is always a similar hole 

 between two contiguous ambulacral pieces, so that the infrabra- 

 chial canals always communicate with the general cavity by as many 

 holes as there are ambulacral pieces. The infrabrachial canals and 

 the branches which they give off are, therefore, merely dependences 

 of the general cavity, divided into two communicating parts by the 



* Comptes Rendus, xciv. (1882) pp. G.58-61. 



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