402 PERCY SLADEN TRUST EXPEDITION 



Hexactinian Larv^. 



The Hexactinian* larvse described by v. Beneden formed two groups : (1) larvee 

 with 8 mesenteries ; (2) larvae with 24 mesenteries ; these larvae he did not name. 

 In 1906 Carlgrenf divided his larvae into four groups according to their mode of life, 

 the arrangement of the tentacles, and the time when the latter begin to develop. 



"A. Larven mit einem pneumatischen Apparat, mit vielen Tentakeln und vielen 

 Mesenterienpaaren : die Minyaden. (Nicht in nordischen Meereu angetroffen.) 



B. Larven, die parasitisch an Medusen leben, und also nur in zweiter Linie ein 

 pelagisches Leben fuhren. Die Tentakeln werden in dem Achtmesenterien-stadium 

 angelegt. Alle sechs Exocoeltentakeln des Halcampulastadiums sind in dem Stadium 

 mit acht Tentakeln vorhanden. 



0. Larven, die wahrend langerer Zeit pelagisch leben und die bis zu einem Stadium 

 mit zwei Mesenteriencyklen keine Tentakeln entwickeln. 



D. Larven, die als solche ein kiirzeres Leben haben und die in dem Achtmesenterien- 

 stadium Tentakeln ausstulpen. Nur zwei Exocoeltentakeln des Halcampulastadiums sind 

 in dem Stadium mit acht Tentakeln vorhanden." 



Li the collection there are six different types of larvas which probably belong to the 

 Hexactiniae, and if so, according to Carlgren's divisions, they should all be placed in 

 group C. Of these six larvae, two have 8 mesenteries, three have 12, and one has 20, and 

 all are without tentacles. 



It is impossible to classify them generically and specifically. All that can be said 

 is that they are probably all different species and that the larvae with more mesenteries 

 do not represent older stages of the larvie with fewer mesenteries : apparently they are 

 not the same species as ariy that have been so far described. 



The chief points of interest are the presence of embiyos in one of the specimens 

 with only 8 mesenteries and the peculiar relation of the mesenterial filaments. 



Larv^ with Eight Mesenteries. 

 8. Larva I. (PI. 24, fig. 16.) 



The larva is white and subspherical, its aboral end produced into a hollow pro- 

 tuberance ; its length is "5 mm. and diameter 75 mm. There are eight radiating grooves 

 on the peristome. 



Eight complete mesenteries are present, continued to the base but little projecting in 

 that part ; with their well-developed muscles they have the Edwardsian arrangement. 

 Filaments are present on all, but on the directives they only extend through a few 

 sections ; they are much convoluted on the ventro-lateral mesenteries. Epithelial cells 

 are found on the enterostomal wall within the mesenterial chambers, due to the edge of 

 the enterostome either being slightly turned up or having slightly grown up. The 

 filaments are connected with this epithelium, which also grows up orally on the dorsal 



* Plankton Expedition, Les Anthozoaires, 1898, pp. 150 and 183. 

 t Nordisohes Plankton, Zoantharien Larvse, xi. 1906, p. 80. 



