AMATOMY OF IIOLOTHURIANS. 131 



testine. A fluid containing nucleated cells fills both the 

 pseudo-hsemal and water- vascular canals. 



Holothuria floridana Pourtales is a large, dark-brown 

 sea-cucumber, with the feet scattered irregularly over the 

 body, and with smaller tentacles than in Pentacta, which is 

 abundant just below low-water mark on the Florida reefs, 

 and grows to about fifteen inches in length. The aliment- 

 ary canal is filled with foraminifera and pieces of shells, 

 corals, etc. ; it is about three times the length of the body, 

 and ends in a much larger coecum than that of Pentacta. 

 There are two widely separated branches of the " respira- 

 tory tree," one being free, and the other, tied to the body- 

 walls by thread-like muscular attachments, extends to the 

 pharynx. The pharynx is calcareous, while in Pentacta it 

 is muscular. On the madreporic body is a group of about 

 thirty pyriform stalked bodies, the longest, including the 

 stalk, about a quarter of an inch in length. Succeeding 

 these bodies, and situated on the madreporic canal, leading 

 to the ring-canal, are a large number of Polian vesicles, the 

 largest one an inch in length. The duct passes spirally 

 nearly round the oesophagus, and empties into the ring- 

 canal by the ducts nearly a quarter of an inch apart. In 

 connection with the tentacles or branchias are twenty long, 

 slender tentacular ampullae, not present in Pentacta and 

 Tliyone. The ovarian tubes are very small, some enlarging 

 and bilobate at the end. 



Closely allied in external form to Holothuria floridana, 

 though belonging to a different family (including Pentacta\ 

 is Tliyone briareus (Lesueur), which lives just below tidal 

 marks, from Long Island Sound to Florida. In this genus 

 the ambulacral feet are not arranged in rows, but scattered 

 over the surface of the body. This species is very common, 

 and as it is more accessible to the student than any other of 

 the sea-cucumbers, we give some points in its anatomy as 

 compared with Pentacta, with which it is more c.osely allied 

 than to Holothuria. In a specimen about eight centi- 

 metres (three inches) long the intestine is over two metres 

 (about seven feet) long, the oesophagus opening into an 

 oval stomach less than an inch in length. The tentacles 



