98 Dr. G. C. Wallich on the Thalassicollida?. 



views therein published are those from which our know- 

 ledge of the true physiological relations of that family may 

 be said to have been almost exclusively derived. But it is 

 asserting too much to say that the Thalassicollidaj were 

 previously unknown, inasmuch as they are not only amongst 

 the most constant but the most numerous inhabitants of the 

 surface-waters of both tropical and subtropical seas. Every 

 voyager who has traversed such seas must have become 

 familiar with their appearance, as I confess myself to have 

 been for twenty years and more. But so far from detracting 

 from the credit due to Professor Huxley's researches, this 

 fact serves only to increase it. In short it was the difficulty 

 of resolving the nature and relations of the organisms under 

 notice that caused them to be entirely neglected, although they 

 must have been constantly met with by other naturalists. 



If we discard as untenable the separation of the isolated 

 forms of Thalassicolla from those which are grouped together 

 in a common gelatinous matrix, " like an animal PotmeUa"*, 

 the soft body may be described as a mass of granular proto- 

 plasm, presenting a well-defined nucleus and contained within 

 a membranous capsule, the latter being in turn protected by 

 a more or less thick gelatinous exudation, whilst numerous 

 sarcoblasts of varying size occur scattered through the endosarc, 

 and occasionally a few may be seen suspended within the 

 external gelatinous stratum. Again, if we compare those 

 forms in which the siliceous framework is composite (that is to 

 say, in which a number of spicular masses afford the required 

 support by being crowded together, as they do in a Sponge or 

 Holothuria) with those in which it is simple and consists of a 

 delicate foraminated shell, we shall find that the relative 

 positions of the hard and soft structures are nevertheless the 

 same, and that the former, when present, invariably occur 

 externally to the membranous capsule, and within the gelati- 

 nous investing layer. 



Owing to the peculiar configuration of the Thalassicollida}, 

 and the facilities afforded by the composite forms for comparing 

 a number of individuals under precisely similar conditions, 

 they are admirably adapted for showing whatever changes take 

 place in the protoplasmic substance as the age of the organism 

 increases ; for although it is very unusual to find any important 

 difference in the degree of development attained by the various 

 members forming one of the composite Thalassicollida?, and 

 there is every reason to believe that their growth is uniform, 

 the constant recurrence of certain characters in conjunction 

 with the evidence of immaturity derivable from small size 

 * Huxley on Thalassicolla, I, c. p. 434. 



