74 THE VICTORIAN NATURALIST 



(9.) The next stage consists in the elongation of the embryo 

 into a tubular form when it becomes flattened at the top and 

 perforated by an osculum. The walls are pierced by pores, 

 spicules appear in the gelatinous layer and the ciliated cells 

 develop into collared cells. This is known as the olynthus stage. 

 (PL I., B. 5, 6). 



(10.) Special chambers are gradually budded out from the 

 gastral cavity and the collared cells become restricted to these 

 chambers, the gastral cavity being lined by a layer of flattened 

 ectodermal cells. 



SOME PECULIAR HABITS OF CRABS. 



By O. A. Sayce. 



{Read before the Field Naturalists' Club of Victoria, 9th July, 1900.) 



Apart from the structure of crabs, which is often . very curious, 

 their habits are frequently of striking interest, as for instance 

 amongst the Oxyrrhyncha, or sharp-snouted crabs, many of them 

 exhibit the peculiar habit of clothing themselves with foreign 

 substances, such as pieces of sea-weed, hydroids, and such like, 

 in imitation of their surroundings,'and so mask themselves from 

 their enemies and their prey. 



A cursory view of one of these crabs would suggest the idea 

 that the foreign material had grown on the animal, but this is not 

 so, for over the body and legs there are series of strongly curved 

 hooklets, and many records are published that explain how the 

 pieces required are snipped off and fastened on to the animal's 

 hooks. Perhaps one of the most interesting records is that of 

 Mr. David Robertson, a reliable naturalist of Scotland, who 

 found, according to Stebbing, that his specimens of Hyas were 

 capable not only of dressing but of undressing themselves. Of 

 the effectiveness of their disguises he had often had practical 

 experience, when upon visiting his aquarium in the morning he 

 was unable to find specimens which he had placed there over- 

 night, and which he had at first thought must have escaped. 

 Close inspection and the help of a magnifying glass, however, 

 would always show that they were present, but that they had so 

 decked themselves out with the vegetables and animals around 

 them as to lose all invidious prominence. By transplanting into 

 an environment of sponges some that had clothed themselves 

 in bright-coloured algae, he ascertained how accurately they 

 knew their business, for they laboriously picked off the gay 

 colours and stuck themselves over with fragments of sponges in 

 their places. 



We have several species in our waters that perform this 

 peculiar habit, and I exhibit a few to-night which are clothed 

 with foreign materials. One very fine and large species, which I 



