VIRGULABIA MIHAllII.IS. 71 



during May and June he found numbers of cgj^s at the bottoms of the 

 glasses in which he kept his specinions ; that from these egfjs larvse in 

 the form of free-swimming cihated planulae were developed, which after 

 a time attached themselves by one end and produced tentacles, a 

 stomach, and four septa, lie kept these young specimens for a month 

 without their undergoing any further change. 



By means of fertilised ova and the free-swimming larvae to which 

 they give rise new colonies of Viraularia are started. Increase in size 

 of the colony, when once started, is effected by the formation of leaves 

 one below another, as already noticed. The actual process of formation 

 of the polypes is easier to study in Virgularia than in the other genera, 

 because by making a series of transverse sections through the lower 

 end of the rachis at different levels all the successive stages of develop- 

 ment can readily be obtained from a single specimen. 



At the very bottom of the rachis there is no trace of polypes at all, 

 and at this part the fleshy substance of the rachis, which is here of 

 considerable thickness, is hollowed out to form the large lateral 

 chambers already described. 



A little higher up we get the first rudiments of the polypes. These 

 appear as transverse rows of small pit-like depressions of the superficial 

 layer of ectoderm which clothes the whole rachis (Fig. 6 dv). Each pit 

 opens by its mouth on to the surface ; its inner end, which is closed, 

 projects somewhat into the lateral chanabers of the rachis, as shown in 

 the figure. Each of these pits will become the stomach of a polype, 

 the mouth of the pit remaining as the naouth of the polype. 



We have already said that the pits are arranged in transverse rows ; 

 each row is situated on one of the slightly marked transverse ridges 

 which mark the commencing leaves at the bottom of the rachis ; and 

 in each row there are seven or eight polypes according to the number 

 present in the fully developed leaves of the same individual. In each 

 row, also, the polypes gradually increase in size from the dorsal to the 

 ventral surface. 



A little higher up in the rachis, i.e., at a slightly later stage of 

 development, we find the pits somewhat deeper; we find, also (Fig. 6), 

 that the lateral chambers have become divided by radial partitions 

 into smaller chambers, one for each pit, which become the body- 

 cavities of the polypes. These body-cavities grow up round the pits, 

 leaving them attached to what are now the body- walls of the polypes 

 by the eight septa or mesenteries. Round the mouths of the pits a 

 series of small buds begins to appear, the rudiments of the tentacles. 



The constrictions separating the leaves from one another become 

 more and more marked, so that the leaves gradually acquire indepen- 

 dence of one another ; the tentacles grow rapidly in size, and develop 

 along their inner borders the pinnules ; the walls of the pits, or the 

 stomachs of the polypes, become thrown into the folds characteristic 

 of the adult polypes, and the bottoms of the pits become perforated, 

 thus placing the stomach-cavities in communication with the body- 



