tlie ripe sperm sacs of the males which are 

 always milky white in colour, and can therefore be 

 readily distinguished from the ova, discliarg-e great 

 (piautities of spermatozoa into Ihe body cavity, and thence 

 1)V wav of the iiiouiii into the water. Fertilisation is 

 most prohal)ly effected in the water, and not in the body 

 cavity of the female just before the discharge of the o\a. 

 If this is the case, the sexmil act is a true process of 

 s])awning. 



The exact time of s])awning may vary in different 

 localities. In the Plymouth district I have found, as a 

 result of a six years' seiies of obseivations, that the 

 spawning always occurs dniing the last fortnight in 

 December and the lirst fortnight in January, and at no 

 other time of the year. At Port Erin the spawning may 

 be somewhat later, as I have examined larvae captured 

 with the Plankton at ]*]aster, which I feel certain are the 

 laiva' of Alci/iniiiiin J if/itdtiim. 



Anatomy of the Colony. 



When a colony of Ahyonium is cut across (Plate I., 

 tig. 5) it will be seen to consist mainly of a number of 

 parallel tubes peiforating a semi-transparent gelatinous 

 !sul)stance in which a number of snndl calcareous spicules 

 are imbedded. J'^ach of these tubes is the bod\' cavitv — 

 or cocdenteion— of a polyp, and the gelatinous snbstani'c^ 

 is ihe mesogloea of the polyps fused together into a 

 common mass. 



When the colony is alive and in a health}' condition 

 a number of delicate transparent polyp heads protrude 

 from the surface of the colony. Each of these is provided 

 with a mouth and eight pinnate tentacles, and the body- 

 wall below the crown of tentacles encloses a single large 

 cavity, which is continuous with the cavity of the tubes 



