EARLY LARVAE 345 



The first three buds appear in surface view as short transverse folds (Text-fig. 23 A, B, d, e). On 

 the sloping aboral side of the ampulla of II (Text-fig. 23, d) arises the gastrozooid of cormidium II 

 (P 3 in Okada's notation). From now on, the rate of growth of cormidium I is speeded up relatively, 

 the gastrozooid of its first group becoming Okada's P 4. 



The identity of Okada's polyps, therefore appears to be : 



P 1 Gastrozooid of cormidium III 



P 2 Gastrozooid of cormidium VII or VI 



P 3 Gastrozooid of cormidium II 



P 4 Gastrozooid of cormidium I 



P 5 Gastrozooid of cormidium IV (or V) 



The points of interest that have come out of my examination of Dr. Dodge's larvae are as follows: 



(1) The final main pattern found in, say, a 10-in. specimen of Physalia, namely of buds arranged 

 in seven main and five or more oral cormidia, each consisting of repeated triple groups of gastrozooid, 

 tentacle and gonodendron, does not arise regularly in orderly progression. As in other suborders of 

 siphonophores certain buds develop precociously. 



The first of these secondary buds to appear are three in number: the gastrozooids of the main zone 

 cormidia III and VII, and the ampulla of the tentacle of cormidium II, which forms the main 

 tentacle. 



(2) The fact that the oral zone of cormidia does not appear at first is due, probably to the fact that 

 the first three precocious buds leave no room for it, so that its five, somewhat reduced, cormidia 

 appear as an after-thought. 



(3) Right- or left-handedness appears almost as soon as the first three buds, which are formed in the 

 same longitudinal meridian as the larval (protozooid) tentacle. This larval tentacle must stream out to 

 one side or the other as soon as the larva surfaces, and the three buds lie just below the surface on that 

 same side (Text-fig. 23 A, b). The tentacles of early formed cormidia such as I and II, which soon 

 follow, appear on the under side of the cormidial primordia, and the gas-gland very early takes up an 

 asymmetrical position towards the under side. These two phenomena enable the observer to see 

 whether an individual larva will become a left- or right-handed specimen, even where it measures 

 only a couple of millimetres in length, and before there is any sign of the future crest. 



(4) The first indication of the future crest is the appearance of two or three little dome-shaped 

 projections from the upper surface of the air-sac (Text-fig. 24 c). 



(5) The secondary buds can soon be seen to form an oblique line, the aboral one rather lower in the 

 water than the oral one. The gastrozooids of III and VII lie above the rudiments of cormidia IV and 

 V. These are formed a little later and are not so easy to see because of being crowded out by the 

 precocious ones III and VII (Text-fig. 24 A, b). 



(6) The gastrozooids of cormidia I and II can be seen quite clearly to develop on the aboral sides 

 of their respective tentacles, whose formation tends to precede them (Text-fig. 24 c). 



(7) There is often a quantity of dark pigment-granules in the endoderm of the air-sac. It surrounds 

 the pore, but not symmetrically, and assuming that this pigmented area must be uppermost as in other 

 siphonophores, it would seem that when the pigment is first formed the larva is orientated with its 

 long axis neither vertical nor horizontal in the water, but at an acute angle to the surface. My belief 

 is that this pigmented area round the pore of a siphonophore saccus in some way utilizes the light 

 energy to control the contraction of the sphincter-muscle controlling the exit of gas according to the 

 intensity of the light and the depth from the surface. The extent of the sphincter-muscle can be 

 judged by its freedom from nematocysts which cover the rest of the larval body. In most of the 

 specimens examined the pore was closed. 



