1871.] WOOBWARD XIPnOSUEA. 49 



the female either in an egg-pouch, or marsupiam, formed by a mo- 

 dification of a certain number of pairs of appendages, or adhering 

 by a viscous secretion to the hairs of the abdominal feet (as in the 

 Crab, Lobster, and Prawn), until they are hatched. 



The ovipositing of Limulus may serve to explain the origin of the 

 masses of fossil eggs met with in the shales of the Old Ked Sand- 

 stone of Forfarshire and of Trimpley, near Bewdley, Worcestershire, 

 formerly called Parlca decipiens, and now roferTedto Pteri/gotits ; for 

 the Eury[)terida, like the Xiphosura, may also have left their eggs 

 in the shallows to hatch. 



From the experiments of Dr. Lockwood it would appear that the 

 eggs of Limulus are slow to hatch. Thus a batch which ho pre- 

 served occupied seventy days after spawning before hatching* ; 

 whilst some, set aside at the end of the season in a jar of salt water, 

 hatched out after some three hundred and fifty days from the time 

 of spawning. 



He very justly estimates the rate of hatching to be due to the 

 greater or less exposure to light and warmth and to the oxygenation 

 effected by the constantly shifting tide-wave and the occasional ex- 

 posure in damp sand or mud to the sun's rays at low water. 



This exceeding vitality and fecundity may best explain the per- 

 sistence of this genus in time, a persistence probably unsurpassed 

 by any among the Crustacean class, save the Entomostraca alone, 



EmhryoJogy of Limxdxis. — We are in possession of thi'ee sepa- 

 rate accounts of the embryology and larval development of lAmti- 

 lus — from the Eev, Samuel Lockwood, Dr, A. S. Packard, jun., and 

 Dr. A. Dohrn, The last of these is the most elaborate treatise, and 

 gives the most carefully prepared figures, I will beg leave to select 

 as complete an account as possible from the two latter writers, Dr, 

 Lockwood being unable to carry on a microscopic examination, a 

 disability we all must regret, inasmuch as he was resident all the 

 summer on the coast, and had hundreds, if not thousands, of fer- 

 tilized eggs to experiment upon in his hatching-jars. His draw- 

 ings, however, are full of interest. 



The eggs measui'e "07 of an inch in diameter, and are green in 

 colour. Each egg is enclosed in a double skin — the thick outer one 

 called by Dohrn the " exocliorion " (J)), the inner the "chorion" (a) 

 (by Packard the outer the " chorion,^' and the inner the " amnion " 

 and also the " blastodenn-sJdn") . (See page 50, fig. 16,) 



The earliest stages were noted by Packard. " Only one or two 

 eggs were observed in process of segmentation. In one the yelk 

 was subdivided into three masses of unequal size. In another the 

 process of subdivision had become nearly completed," 



1st stage. — " In the next stage observed, the first indications of 

 the embryo consisted of tJi7'ee minute, fiattened, rounded tubercles — 

 the two anterior placed side by side, with the third immediately 

 behind them. The pair of tiibercles probably represent the first 

 pair of limbs, and the third single tubercle the abdomen," 



* Dr. Packard makes the time of hatching six weeks only. 

 VOL, XXVIII, PART I. E 



