394 POLYZOA HYrPOCREPIA. 



these bubbles, the ova, which at this period are loose and floating in 

 the tubes, are gradually elevated and conveyed to the exterior. In 

 November many of the specimens were seen with air-bubbles and 

 ova successively escaping, and the external surface was covered by 

 ova thus conveyed to the exterior. Those specimens which were 

 black and putrid, and appeared to have been dead some time, ex- 

 hibited the horny tubes nearly devoid of ova. After a time the 

 horny basis itself becomes softened, and appears to undergo decom- 

 position. During the following spring, according to the evidence of 

 Vaucher and Raspail, the horny envelope of each ovum separates 

 into two lateral halves, adhering on one side as by a hinge. From 

 these valves a small gelatinous tubercle projects, which soon expands 

 into a distinct polype, and gradually becomes elongated into a 

 tubular form. From the sides of this tubular polype, small gelati- 

 nous buds soon appear, and these again become developed into 

 distinct polypes; the tubular parietes gradually become consolidated, 

 and form the horny basis of the mature Alcyonella." 



The Alcyonella, if I have correctly sorted the synonymes, was 

 discovered by Trembley in the spring of 1741. It seems necessary 

 to give a copy of his figures here (wood-cut, No. 73), since on them 

 is founded the second variation of the species, and they exhibit it in 

 a guise very different from that represented in our Plate 74. His 

 history of the animal is marked with much of that excellence which 

 distinguishes the inquiries of this naturalist. He correctly describes 

 the connection and relationship between the polype and the common 

 mass; the arrangement of the tentacula, and the structure of the 

 alimentary canal, although he failed to detect the anus. He over- 

 looked the cilia of the tentacula from employing magnifiers of too 

 low a power, and attributed the whirlpools created in the water by 

 their play to the motion of the tentacula themselves, which he says 

 were also used separately to force the animalcular prey into the 

 mouth. He knew that the polypes were not contractile, and be- 

 lieved their retraction within the tubes was dependent on the play 

 of a muscular thread which descended from the body in the common 

 mass.* The gemmiparous mode of increase in the polypidom is also 

 detailed with some minuteness, but he had not seen the ova, at least 

 in a state of maturity, f 



* Professor Allman thinks that the organ which Trembley took for a retractor 

 muscle is an ovary. On Paludicella articulata, p. 8. 



t It is even doubtful whether the bodies he took for immature ova were really so. 

 " J'ai vu dans plusieurs dcs Polypes a Panache, sur lesquels j'ai fait mcs observations, 



