REPORT ON THE SIPHONOPHORjE. 339 



The family Physalidse was established in 1835 by Brandt (25, p. 36). He first 

 distinguished two different subgenera in the genus Physalia, viz., (l) Scdacia (or Phijsalia 

 proper), with a chambered dorsal crest of the float; and (2) Alophota, without crest. This 

 distinction, although not accepted by later authors, is very important, since the crestless 

 state of the pneumatophore, regarded from a phylogenetic point of view, must necessarily 

 precede the crested state. There still exist also to-day small Physalidae which reach 

 sexual maturity in the crestless state. We establish for these the subfamily Alophotidae, 

 and oppose it to the crest-bearing subfamily Caravellidse. Among the small Alophotidse, 

 as well as among the large Caravellidse, occur two different forms which may be distin- 

 guished as genera ; one of these (Alophota and Physalia) bears only a single large main 

 tentacle, besides numerous small accessory tentacles ; the other group (Arethusa and 

 Caravella) bears numerous large main tentacles of nearly equal size (besides the small 

 accessory tentacles). 



The distinction of species in these four genera of Physalidae is a very difficult task, 

 since the entire family is transformistic, and all the so-called " good species " are 

 connected by Darwinian intermediate forms. Nevertheless there exist a number of 

 " geographical species " as local forms in the different seas. In the majority of the 

 numerous descriptions the species of Physalidse are founded upon slight differences in the 

 variable coloration, or different states of contraction of the very variable pneumatophore 

 and other parts (compare Huxley, 9, p. 99, and Chun, 83, p. 557). A better and more 

 natural distinction of " relatively good species " will be got when the future observers 

 carefully regard the following anatomical structures : — (1) the grouping and composition 

 of the monogastric or polygastric cormidia ; (2) the relation of the basal protosiphon (at 

 the distal end of the float) to the secondary siphons (or metasiphons) on its ventral face ; 

 (3) the difference in structure and form of the pneumatophore, mainly at its apical and 

 basal poles ; (4) the structure of the crest, the number of its chambers, &c. 



Cystonula-Larvse. — The organisation of the large adult Physalidse, with their com- 

 plicated structure and composition of hundreds of polymorphous parts, is so difficult to 

 conceive, and seems to be so widely different from that of other Siphonophorse, that it 

 has led most authors to many erroneous opinions. To arrive at its true understanding, it 

 is indispensable to regard carefully and compare critically the smallest and simplest forms 

 of this peculiar family, and especially the youngest larvae with a very simple structure 

 (Cystonula, PL XXVI. figs. 1, 2). The first larvae of a very young stage were described 

 in 1859 by Huxley (9, p. 102, pi. x. figs. 1, 2). I myself had in 1866, in Lanzerote, the 

 opportunity of observing living a number of similar larvae and of comparing them with 

 the simplest and oldest genus of the family, Alophota (PI. XXVI. fig 3), and with 

 the more highly developed Arethusa (figs. 4-8). Recently Chun has published some 

 interesting notes on young Physalidse (83, p. 558). 



The smallest and youngest Cystonula, which I observed in December 1866, is figured 



