390 Royal Society. 



liest stages of development, together with the vesicle and the mem- 

 branes of the ovum at a later period, as showing in this low form of 

 animal the conformity of structure and laws with those which pre- 

 vail in the higher forms. 



In the third section, the author speaks of the deposition of the 

 ova, and of the habits of the species, as observed in specimens col- 

 lected and preserved by him for that purpose. These habits he re- 

 gards as particularly curious. The female excavates for herself a 

 burrow, by digging with her mandibles in the soil, which she has 

 previously moistened with a fluid, supplied, as the author believes, by 

 her immense salivary glands. With this she forms a soft pellet, which 

 she removes from the burrow with her mandibles and anterior legs ; 

 and thence, after being brought to the top of the hole, it is passed 

 on to the next pair, and by these on to the next in succession, until 

 it is entirely removed out of the way ; after which, she deposits her 

 eggs and closes the burrow with moistened clay. Great difficulty was 

 experienced in preserving the eggs during the observations, from 

 the circumstance that their shell is soft, and dries quickly when ex- 

 posed to the air. To avoid this, the author had recourse to the plan 

 of inclosing the eggs in a glass tube, filled with clay, and closed 

 with a cork ; the eggs being placed in a cell next to the glass. 



The fourth section, which constitutes the most important part of 

 the paper, gives the history of the evolution of the embryo. The 

 process is divided by the author into different periods. After a few 

 observations on the earlier changes of the egg, and the proof that they 

 consist in an alteration in the size and appearance of the cells out of 

 which the embryo is formed, he states his having observed that the 

 egg bursts at the end of twenty-five days, by means of a fissure along 

 the dorsal surface, as described by Savi and Waga ; and that, in oppo- 

 sition to the remarks of Degeer, the young Julus, as first stated by 

 Savi, is perfectly apodal. The author has also discovered a singular 

 fact, entirely overlooked by all who have attended to the development 

 of these animals, namely, that the young Julus at this time is still an 

 embryo, and is completely inclosed in a shut sac, which terminates 

 in a distinct funis at the extremity of the body, and in the proper 

 amnion, or foetal envelope of the animal. He finds, also, that the funis 

 enters at the posterior penultimate segment of the dorsal surface of 

 the body, and not at the dorsal surface of the thoracic region, as 

 seen by Rathke in the Crustacea. The embryo, he says, is retained 

 in connexion with the shell, between the two halves of it, for seven- 

 teen days, by means of the funis, which is continuous with a second, 

 or external membrane, the chorion, which lines the interior of the 

 shell. He states that the liberation of the embryo from the shell is 

 not effected by any effort of its own, but by the expansive force of 

 the growth of its body. He describes, also, another important fact 

 which had been overlooked by previous observers, relating to the mode 

 and place of origin of the new segment of the body in the Julidse. 

 The new segments are always produced in a germinal membrane im- 

 mediately before the penultimate segment, which segment, with the 

 anal one, remains permanent throughout the life of the animal. The 



