110 Tranmctions of the 



an artificial and not a natural appearance is easily seen by apply- 

 ing a small quantity of water, when the bodies in question begin 

 to swell up, a distinct thread appears round the circumference, 

 they burst, and this thread alone remains as evidence of the pre- 

 vious existence of a zoosperm. 



The zoosperms of Phalangium eornvtum (Fig. 10) resemble 

 those of Epeira in being simple disks without any appendages; 

 they are circular, and have very thick highly-refracting borders 

 with a bright centre. Although resembling the zoosperms of Epeira 

 in form, they must have a different composition, as they do not burst 

 either from remaining on the slide or from the addition of water. 



I have not had much opportunity of investigating the zoosperms 

 of theEchinodermata, but I have examined one species of Starfish and 

 one Holothurid. The Starfish, Asteropecten crenaster, possesses zoo- 

 sperms of the linear form (Fig. 11). The caput is a spherical body, 

 which varies in size in difierent specimens ; in the centre there is a 

 more or less bright spot : in diameter the disk measures ' 002 mm., 

 sometimes more, sometimes less. The tail is of excessive tenuity, 

 and generally measures about fifteen times the diameter of the head. 

 After the zoosperm has remained some time on the slide the caput 

 swells up, and takes on the appearance of a vesicle, having a highly- 

 refracting somewhat square particle placed on its circumference, 

 which particle appears to be the remains of the bright spot which 

 occiipied the centre of the caput.* 



Holothuria tubulosa, a species which is very common about 

 the shallow parts of the bay of Spezia and at Leghorn, has 

 zoosperms somewhat resembling those of the Asteropecten, but 

 larger and more active. The head jerks from side to side, often 

 without making any progression ; the vibration is so extremely 

 fast, that the caput frequently appears double ; at other times they 

 advance violently, and then suddenly stop ; others make excursions 

 in a circular or serpentine course ; altogether they give one more 

 the impression of independent animals than organic units ; such 

 motions have even caused writers to attribute volition to monads. 

 The caput of this species of zoosperm (Fig. 12) consists of a globule 

 of highly refracting matter, with strong thick walls which are dark, 

 and in the centre there is a bright spot. The caput generally 

 measures • 004 mm. in diameter. The tail is long and of extreme 

 tenuity, and it averages from ten to twelve times the diameter of 

 the head; but the measurements of such mobile and fine lines are 

 so difficult that they can scarcely be depended upon for exactitude. 

 Like the zoosperms of Asteropecten, these imbibe fluid after death, 

 and take the form of a vesicle, to the wall of which is attached a 

 small rounded highly-refracting particle, the tail having disap- 

 peared (Fig. 12 a). 



* Sea-water effects this oliauge much more quickly. 



