31 



when, not having this organ (which the adult uses so effectively in such emergency), the 

 little thing begins a vigorous flapping of the branchial plates. This causes it to rise in 

 the water ; then, by ceasing the agitation, it at once descends with a chance of alighting 

 right side up "*. Eighty-two days after spawning, a young Limulus moulted. " A few 

 minutes sufiiced for it to withdraw itself from its baby-suit ; in this act it rested a little 

 while, with the caudal appendage, now formed, only half withdrawn from the old 

 shell" f. 



The extricated animal is ^ of an inch in width, and its tail is -^ of an inch in length. 

 The tail is formed bent under the thoracetron, is at first curved, and " requires some 

 hours to straighten out "%. The setaceous fringe of the thoracetron is replaced by teat- 

 like or half-developed spines. The spiny fringe of the cephaletron is gone. The tail is 

 at first somewhat stumpy, almost ovoidal in transverse section, " more distinctly marked 

 with lines of segmentation than is that of the adult "§. As the young Limulus " tra- 

 velled on the mud before this moult, it made tiny rows of toe-tracks, leaving a plain 

 unmarked space between the rows. Noio it moves with tail depressed, and makes a 

 median line, dividing the toe-tracks into two series " ||. 



The year following the collecting of the ova, Dr. Lockwood records the interesting fact 

 that certain ova at the bottom of one of the jars, " which had never been in contact with 

 the sunlight," still retained the embryo alive and revolving; these having been trans- 

 ferred to " new sea- water and clean sand, with a good exposure," were hatched ; and the 

 larval Limulus left the egg within two weeks of a year after oviposition and impregnation 

 of such G^^ ^. 



Dr. A. S. Packard**, from observations on impregnated ova of Limulus, transmitted to 

 him by Dr. Lockwood, adds details of intraovular steps of development, and gives accept- 

 able figures of these and of the excluded larva. 



Formifaction aggregates the protoplasmal beginning of the ovum into a central mass 



Fis. 1. 



Fiar. 4. 



Fiar. 2. 



Cell-egg 

 (Pkd. pi. iii. fig. 4), 



Portion of surface 

 of impregnated 

 egg (Pkd. pi. iii. 

 fig. 7). 



Section of egg- walls 

 (Pkd. pi. iii. fig. 9). 



7«it 



Embryo with limb-bnds 

 (Pkd. pi. iv, fig. 1). 



of larger and denser granules, constituting the nucleus (cut, fig. 1, b), within which is 



• Lockwood, Inc. cit. p. 263. t Id- ib. t Id. ib. § Id. he. cit. p. 269. 



II In quoting this observation, I am duly impressed by the " caution for the interpreters of the ' Protichnites,' 

 seeing that the same species, at different ages, may make widely different tracks." — Tb. p. 273. 



*1I Id. ib. p. 272. This result recalls the arrest of development of Tadpoles kept in the dark. 



** " The development of Limulus polypTiemus" in Memoirs of the Boston Society of Natural History, vol. ii. 1872. 

 (This excellent memoir was read November 16th, 1870.) 



