154 NATURAL HISTORY OF OUR SHORES 



have not seen, and do not know whether it is antecedent 

 or subsequent to the date above named. 



In this, Dromia has also been rightly placed with the 

 Brachyura forming a division. 



The Brachyura (short-tailed or true crabs). Before 

 we enter into the consideration of the different species 

 of those that are found on our shores it will be well 

 to survey their development, and the changes which they 

 undergo before they reach the adult form, changes which 

 may almost be likened to the " larva," " pupa," and 

 " imago " stages of insects. 



We will take the common shore crab for an example. 



At certain seasons, attached to the swimmarets of the 

 female (the swimmarets are the oarlike appendages on 

 the under side of the abdomen, strongly developed in the 

 prawn, lobster, etc., and aborted or modified in the short- 

 tailed crabs), are a large number of eggs, attached also to 

 each other in little clusters by fine threads, the result of 

 the coagulation of a gummy substance which is extruded 

 with them. 



Hatching takes place while the eggs are attached, and 

 the young crabs, in form quite unlike the parent, roll help- 

 lessly on the sea bottom for a little while, but they rapidly 

 gain strength, and after a few tentative efforts rise, and 

 swim nimbly away, with little spasmodic jerks. 



Little folds of membrane on their back and at their an- 

 terior end are pressed from within until they form long spine- 

 like processes and the young (a 7,oea, it is called) is of the 

 form shown in Fig. 63. It swims nimbly in the sea, usually 

 near the surface, in this form for two or three weeks, feeds 

 greedily and changes its coat repeatedly. Then after a 

 time its spines disappear and it resembles a crustacean of 

 the Macruran or long-tailed type, such as the lobster, etc., 

 only it is broader in proportion. 



It has exchanged its swimming feet for claws and walking 



