53 



ffitudinal coat in rotaininj^ the tubes to their proper sizR. 

 Tlie first or inn«n' tunic appears to be of a serous cliaractcr, 

 and to resemble the lining membrane of arteries ; but has this 

 character in addition, that it is the sole seat of reproduction 

 in the order. 



The spicula are dispersed irretpilarly tlirousrh the sub- 

 stance of the pol3'pe mass; near the surface far mors 

 sparingly than towards the centre, where they are more 

 closely aggregated. They are very irregular in shape, but 

 yet all possess a character in common, tn many cases they 

 closely resemble the bodies described in the Gorgonia, and 

 have a similar formation. Some are K-shaped in various 

 disfigurations of its parts. By maceration they readily 

 undergo decomposition, and are then found to have the sanie 

 cellular composition as the bodies in the Gorgonia. The 

 cellules are very closely and intimately connected, yet the 

 connection is readily broken by maceration or weak acids. 

 Though they are thus diffused through the fleshy gelatine 

 with but very little organic connection, yet from their com- 

 position they appear to be the result of some vital action. 

 Dr. Johnston considers them as the (irst appearance of a 

 polypidom or axis, he says " that it would not be dillicult 

 to trace them through all their gradations to the horny 

 flexible axis of the Gorgonia." Such, from the observations 

 made on the pitl* and investing membrane of the axis, and. 

 the membrane of the crust in the Gorgonia, may possibly be 

 the case ; but I rather hesitate to consider them similar to 

 the raphides of plants, or the spicula of sponges. 



Reproduction occurs in this order only in one way, by 

 the internal generalion of gemmules or ova. There is no 

 particular set of organs appropriated to this function as in 

 the higher animals; nor is there, as in tiie Hydroidje, a 

 periodical developement of ovarian vesicles. Tbe function 

 appears to be of a difiusive kind, and is common to all parts 

 of the lining membrane of the tubes, and according to au- 

 thorities, to the walls of the abdominal cavity. 



The manner in which the ova are developed is best 

 observed in a transverse section. In a natural state the 

 calibre of the tube is circular, but when ova are about to be 

 developed, a segment of the circle is slightly bulged towards 

 the centre. As developement progresses, the bulging in- 

 creases and becomes uiore and more circular, till it becotiies 

 quite globular and lies on t'te tube as a tangent. Tiie ovum 

 is held to the lining menibriine by an umbilical cord, which 

 is soon clearly to be noticed; this gets more and more at- 

 tenuated and is finally absorbed or ruptured and the ovum ia 

 left at liberty in the tube. From the very earliest period at 



G 



