Echinodermata. 



2) a plexus of irrigation canals which surround it and may be called the genital 

 plexus. This is partly identical with the genital plexus of P. H. Carpenter. The 

 first indication of it is a vertical canal which appears between the 2 mesenteric 

 folds uniting the rudiment of the genital stolon to the bottom of the intestinal 

 pouch. The stolon is at first a cellular structure which enlarges into a cavity 

 with folded walls, and gives off the genital cords of the arms from its upper end 

 just as described by W. B. Carpenter. The views of Vogt & Yung regarding the 

 Zooxanthellid nature of the sacculi are not adopted; but Perrier agrees with 

 them in denying the existence of a definite nerve-vessel beneath the ambulacrum. 

 His general views of the physiology of the nutritive processes in Crinoids were 

 noticed in the Bericht for 1885 Ip 184, 187. 



Vogt & Yung give a general account of the morphology of Antedon rosacea which 

 contains some novelties. Within the integument of the disk there lies a super- 

 ficial network of vessels accompanied by fine nerve- fibres. Its meshes contain 

 the heaps of pigment granules. The inner ends of some of the ciliated water-pores 

 lead into these vessels , while others are connected with the mesenteric plexus ; 

 but none open directly into the coelom. The existence of a sub-ambulacral nerve- 

 vessel is formally denied. The water-tubes do not open into the body cavity, 

 but are continuous with the ramified vessels of the labial plexus. The neuro vas- 

 cular axis of the arms consists of a central canal surrounded by a nervous sheath, 

 and often divided vertically by a partition of the same substance. The dorsal 

 organ, which is continuous with the central vascular tube of the chambered 

 organ , is manifestly glandular throughout its whole length , and its glandular 

 structure is continued into its ramifications which are very numerous at its ventral 

 end and join the spongy tissue in the peristome as described by Carpenter. Nerve 

 fibrils are believed to accompany these vessels. The genital tube is not sur- 

 rounded by a vessel, but has a thickening along its ventral edge in which the 

 germs of the reproductive elements are developed. The sacculi contain the 

 zoospores of symbiotic Zooxanthellae, the amoeboid spores of which are the yellow 

 cells that occur so abundantly in the ectoderm of the larva. 



Dendy ( l ) describes a very large individual of Antedon rosacea which has 

 12 arms, owing to the second joint above the axillary radial being itself axil- 

 lary in 2 of the primary arms ; and he suggests that its unusual size may be due 

 to its increased power of obtaining food. 



Dendy ( 2 ) thinks that the evisceration and subsequent regeneration of the 

 lost visceral mass of a Comatula may take place naturally , and that the eviscera- 

 tion may serve to remove poisonous particles or dangerous parasites from the 

 organism. It depends on the separation of the connective tissue covering the 

 aboral surface of the visceral mass from that lining the cup. Regeneration com- 

 mences 1) by a series of outgrowths from the latter and 2) by an ingrowth of 

 connective tissue and epidermis from the edges of the injured area. This last in- 

 creases in size and a new alimentary canal is formed, probably by invaginatiou 

 from its oral end. A complete visceral mass, somewhat smaller and less pigmen- 

 ted than the old one, is formed in 21 days. 



Carpenter ( J ) describes the great variations in the characters of the cirri of 

 Antedon phalangium. Four types may be distinguished which pass into one another 

 by intermediate gradations. A) Long-jointed, from the Mediterranean and Atlan- 

 tic. B) Intermediate, from these localities and also from the Minch. C) Square 

 jointed, from the Atlantic and the Minch. D) Short-jointed, from the Minch. A 

 and D differ greatly in appearance, though containing about the same number 

 of joints. Dimorphic cirri also occur in other European and Arctic Comatulae. 



Levinsen figures a Peutacrinoid larva of Antedon Eschrichtl which has one 



