SYSTEMATIC AND BIOLOGICAL ACCOUNT 67 



Mr Fraser-Brunner's collection (Gulf of Aden). Off Aden (night, 5. xii. 1948) several adult specimens 

 (and five larvae); off Aden (day, 6. xii. 1948) parts of several adult specimens; 20 miles north-west of 

 Bulhar one small specimen with adult (2-ridge) type nectophores. 



'S.V. Cap Pilar' (Seligman collection). At a position in 35 21-5' S., 66° 22-5' E. (to the south of 

 'Discovery II' Station 1754) at the surface on 30 April 1937 an adult specimen was taken bearing 

 twelve to thirteen gastrozooids. 



Larvae. There is no record of larvae having been bred since Haeckel (1869 a, Crystallodes rigidum) 

 watched their development in the Canary Island of Lanzerote in the winter of 1866-7, though Lens 

 & van Riemsdijk (1908) recorded what is probably a series of thirty-four post-larvae of this species 

 under the name ' Crystallomia spec, group I '. Twenty-three of these formed a series, specimens 

 increasing gradually in length from 1-5 to 12 mm. Four of them were in the monogastric stage, but 

 bore no larval bracts, except one which evidently had a bud of one. Lens & van Riemsdijk described 

 the succession of types of tentilla. It will therefore be of interest to illustrate some post-larvae taken 

 by ' Manihine ' in the Gulf of Aqaba Station A 1 (Text-fig. 27). Their specific determination depends 



Text-fig. 27. Larva of Agalma okenii from the Gulf of Aqaba, 'Manihine' St. 1, x 23. 



on the facts that they have trifid tentilla like Agalma spp. and that the bracts differ from those of the 

 only other Agalma species elegans, but agree with those figured by Haeckel for Crystallodes rigidum 

 ( = Agalma okenii). 



The three interesting monogastric larvae bearing larval bracts and a larval type of tentillum were 

 taken at 'Manihine's' Aqaba Station Ai made on 31 December 1948 in 15 fathoms. The smallest of 

 the tentilla measured about 0-2 x 0-13 mm., having three tiny processes at the distal end, one turn of 

 the cnidoband, and a number of nematocysts (0-01-0-06 mm. long) set obliquely at the base (cf 

 Lens & van Riemsdijk, 1908; fig. 98, pi. xm, 'type 1 '). 



Dawydoff (1928) has given a warning that accounts of siphonophore development prior to those of 

 Metchnikoff must be treated with caution. This warning should be extended to Dawydoff 's own 

 short summary, which contains false statements as well as interpretations. The remarkable allegation 

 by Haeckel ( 1 869 a) that the pneumatophore originated as a diverticulum of the common ' Primitivhole ' 

 was by implication denied in 18886, when he said that in all cases the pneumatophore arose as a gland- 

 like invagination of the exoderm. It is very difficult to see the structural details of these siphonophore 

 larvae when they are alive, except in the early stages. I am concerned here only with the larval bracts 

 figured by Haeckel. They have a shape that is characteristic, and is shown in lateral view by Haeckel's 

 (1869 a) plate vn, fig. 51. The upper and outer faces are nearly at right-angles to one another, and 

 the outer face is divided by a longitudinal ridge into two facets (Text-fig. 27). 



9.2 



