THE THALIACEA. 97 



Blastozooid B. 



A single specimen, -which had completely degenerated and i\as in very bad condition, 

 (Exhibited muscle-bands thinner than in those attributed to Trltonis at a corresponding 

 length. It would not have been recorded here, but for the fact that it occurred in tlie 

 same haul as some trophozooids to be described (p. 98). 



DoLiOLrJi Krohni, Herdman. 



Specimens which seemed to agree with Borgert's figures and description occurred in 

 32 A (50 fm., 1 specimen) and 34< c (75 fm., 3 specimens). 



As all hlastozooids are so much alike after degeneration (which in Blastozooid A sets in generally 

 at about 2oO or 2-75 mm. of total length), it is a little difficult to see what criterion can ever be applied 

 to their specific determination, the organs ordinarily used in diagnosis having disappeared. As an 

 experiment in this direction, which I hope may be repeated by someone else iu another species, I have 

 measured the width of the fourth muscle-band in fifty specimens of various lengths, and give in the 

 following table the means (not averaged) at those lengths : — 



!Meau width of muscle- 

 Total length. band iv in /j. » 



3 or more, less than 4- mm 370 



^i „ ., 5 „ 50i 



S „ „ » 575 



„ „ 7 „ SIO 



7 ,, „ ^ 1, '''^O 



8 aud more 1012 



d. Trophozooids. 



Trophozooid a (? = DoLiOLUM Tritoxis, Herdman). (Pi. 8. figs. 2, 3.) 

 In 8 out of the 50 hauls between 100 fjithoras and the surface, which coutaiucd 

 Doliolnmoi any kind, occurred au uiulescribed but characteristic trophozooid, amounting 

 to 100 specimens. It is stated that trophozooids are unable to lead au independent 

 existence ; we may therefore expeci to find the corresponding blastozooid ia 

 the collection. Tlie mere numbers captured indicate a very great probability that 

 this form belongs to the Blastozooid A, which I liave provisionally assigned to 

 IVifon/s. 



The only trophozooids hitherto figured and dcscrihed with any approach to specific 

 certainty are those of Miillerl, Krohn, Ehrenhcrtji, Uljanin non Krohn, and dcnficidaliim, 

 Quoy and (iaimard. At the outset we are met by the dilficulty that the figures of the 

 trophozooid of Jliilleri given by Grobben (j)!. ii. tig. 9} aud Uljanin (pi. xi. fig. 9) do not 



SECONK series. — ZOOLOGY, VOL. X. 10 



