362 PROJ'. E. A, MINCHIN ON THE BRITISH [DeC. 13, 



generally confused it with Glathrina contorta, impossible as this 

 might seem to anyone acquainted with the two species, and con- 

 sidering not only the sharp differences in spiculation, correctly 

 described by Haeckel, but also the complete dissimilarity in 

 external form and appearance between the two sponges ; nothing 

 could be imagined, in fact, more unlike than full-grown colonies, 

 of the two sponge species. 



(a) External Characters. 



LeuGOsolenia coynplicata occurs commonly in either the bushy 

 or the arborescent form. My specimens from Plymouth are all 

 of the former type ; I have it not only from rock-pools along the 

 shore, but also dredged from deep water off the Mewstone. This 

 delicate sponge is rarely found in situations in which it is liable 

 to be left dry at low tide. It forms compact colonies in which 

 numerous closely-set oscular tubes arise from, and partly conceal, 

 a basal growth of finer tubes forming a reticulum attaching it to 

 the substratum. In my specimen from the Mewstone the osculai^ 

 tubes show a marked tendency to assume the characteristic tree- 

 like form, especially towards the centre of the bushy colony. 



The largest specimens of L. complieata that I have seen were 

 collected in the Zoster a-heds, at Roscoff, close to the Laboratory, 

 where this beautiful sponge, favoured by the shelter afforded, 

 grows in profusion and in the most luxuriant manner. As a rule, 

 it does not grow on the Zostera itself but on the stronger and 

 tougher algfe found associated with it. The sponge itself is so 

 fragile that it is scarcely possible even to lift a large specimen out 

 of the water without pieces breaking off, and I have found it 

 impossible to transport them entire. These specimens, and all 

 others which I haA'^e collected at Roscoff, show the typical arbor- 

 escent form by which the sponge can be recognised at a glance, a 

 mode of growth perhaps correlated with the clean granite rocks 

 and sand, and the pure water, very free from mud and sediment, 

 at Roscoff, while in Plymouth Sound the conditions are more 

 estuarine. In the largest specimens from the Roscofl Zostera- 

 beds the arborescent growth differs, in a manner which strikes the 

 eye at once, in different portions of the sponge-colony. In the 

 deeper parts, close to the stems of the supporting seaweed, the 

 oscular tubes form a looser, more straggling growth, apparently 

 due to the fact that they grow more rapidly in length than do the 

 diverticula which arise from them. Higher up the oscular tubes 

 are found growing vertically upwards, and at the same time 

 sending out on all sides a profusion of diverticula which become 

 oscular tubes and throw out other diverticula in their turn, with 

 the result that the sponge assumes the pinetree-like form figured 

 and described by Haeckel from the coast of N^ormandy under the 

 name Ascandra pinus (Monographie, vol. ii. p. 105, vol. iii. pi. 19). 

 Haeckel's figure represents this form faii-ly well, except that, a& 

 usual, he puts more curves into the branches than they should 



