372 LOWER FORMS OF MARINE LIFE 



of its shell while engaged in burrowing into the mud with its limbs. The aforesaid 

 Limulus moluccanus is the longest known representative of the group, although 

 the most curious species is the Chinese L. longispinus, in which the shell is armed 

 with a formidable array of spines. The species shown in the illustration ranges 

 from Maine to Yucatan. It has been proposed to split the group into several 

 genera, and to replace the name Limulus by an older one. 



crabs and The Crustacea form a most numerous tribe, in which the genera 



Lobsters. are t b e counted by hundreds and the species by thousands ; for in 

 this great class are included a vast number of the small organisms forming the 

 plankton of the surface of the ocean, which supplies food to the Greenland and 

 several other species of whales. Crabs and lobsters, to which alone among the more 

 typical groups reference can be made in this place, are excessively fertile animals, 

 as is demonstrated by the following estimate of the rate of propagation of the 

 ordinary lobster and crab on the British coasts. As regards the number of eggs 

 borne by the females of the two species, it is estimated that while the berried crab 

 {i.e. the fertile female) carries on an average about 1,000,000, the female lobster 

 has only about 40,000. In both instances the number increases with the size of 

 the individual. Newly spawned lobsters have been taken in July and August, 

 which indicate that the spawning-season lasts from the middle of July to the 

 middle of September. On the other hand, crabs spawn from November to 

 Januaiy, or possibly the beginning of February. From July to September has 

 been given as the hatching-season of the lobster, and this tallies fairly with 

 Northumbrian records, the lobsters hatching on that coast chiefly between the 

 end of June and the end of August, so that from June to August or September 

 may be given as the season. Crabs are somewhat later, their hatching-period 

 lasting from July to August. Accordingly, while the eggs of the lobster take 

 about eleven months to incubate, those of the crab hatch out in about eight months. 

 When hatched, the fry of the lobster at once betakes itself to a purely pelagic 

 existence on the surface of the ocean, where it remains for about three weeks, 

 undergoing during this period four moults and acquiring some of the characteristics 

 of the adult. At the end of the three weeks the young lobster takes to the bed of 

 the sea. Information with regard to the early history of the young crab is 

 incomplete, but it seems to pass about a month (with four changes of coat) in the 

 so-called zoea stage, after which there is another intermediate stage before the fry 

 takes on a distinctly crab-like appearance and sinks to the sea-bed. 



Female lobsters are mature when about ten inches in length, and to reach 

 these dimensions apparently takes about four or five years. Young crabs of an inch 

 to an inch and a half in diameter are probably about a year old, and the females are 

 about five years when they commence to spawn, at which date they are usually from 

 five to five and a half inches in diameter. As regards seasonal migrations, it appears 

 that crabs leave the coast for deeper water in the autumn ; the same individuals 

 generally returning to the shore during the spring, although a certain number 

 depart from their original haunts to find a new home on another part of the coast, 

 which is always northward. The winter migrations of the lobster are less marked, 

 few going far from the inshore ground, where those with eggs remain throughout 

 the season ; nevertheless, a few are taken far out to sea. The mortality of lobsters 



