602 BULLETIN OF THE BUREAU OF FISHERIES, 
: 
the concession, the construction of pares, the guarding mentioned above, but 
even the cost of manipulation of collectors and larve attached to these. Expe- 
rience shows, in fact, that even on the richest of banks sponges grow at con- 
siderable distances the one from the other; this fact shows us that a great 
number of larve are lost to reproduction, as the sponges emit larve in 
considerable numbers, and if the majority of these came out victorious from 
their struggle for existence we might see among the sponges themselves intense 
vital competition. Such is not the case. Are the larve destroyed because 
only few of them find a favorable spot to which they may attach themselves; 
are few of them capable of living; or is their greater number the prey of their 
enemies? Let us study these three hypotheses separately. 
In regard to the first, it must be observed that the larve possess very 
imperfect means for the seeking of a support; they have no organ of direction. 
When sponge larve are kept in a glass jar their fixing is retarded because glass 
is not a very suitable support; it is accelerated by placing in the jar solid objects 
to which the larve attach themselves readily, as fragments of shells, or even 
by covering the interior of the jar with a coating of collodion.* At the moment 
of the physiological crisis, which acts so radically on their anatomical structure, 
it seems that each larva which does not meet a solid body to which it might 
cling is destined to perish; it must attach itself or die. Do we not see at times, 
in our laboratories, sponge larve spread useless on the surface of the water of 
the jars against the upper layer as they would do against a solid body? If 
our hypothesis is well founded it seems to us that collectors with a large surface, 
disposed around the sponges, would save a great number of larve which in 
their normal course would not meet any bodies to which they could attach. 
We know nothing at all of any of the enemies of the sponge larve. Among 
animals widely utilized by man the sponges are perhaps those the ethology of 
whose larve is least known. We know that adult sponges are respected, 
ordinarily, by almost all marine animals; I saw accidentally, in an aquarium, 
blennies attack Swuberites domuncula and serranids come and bite the parts 
wounded by the blennies. But these are exceptional cases. The immunity 
may be due to the great amount of organic ammonia contained by the sponges. 
How far are their larve left unmolested by other animals? This we do not 
know at all. We see that on bottoms of geological structure and flora identical 
in appearance there are banks rich in sponges separated by zones almost com- 
pletely barren. We have every reason to seek to know why the distribution 
of these sedentary animals is so unequal, and we must observe that the inter- 
relations of animals have not been sufficiently studied from this point of view. 
a] have made this observation quite frequently. This question of the nature of supports offered 
to the larve is of the greatest importance to sponge culture. 
