Mr. J. Lubbock on the Generative Organs in the Annulosa. 411 



ordinary ova to be essentially identical, only that the former have an 

 outer case. The truth is that they are essentially different structures. 

 The true ova are single cells which have undergone a special develop- 

 ment. The ephippial ova are aggregations of cells (in fact, larger or 

 smaller portions, sometimes the whole of the ovary), which become 

 enveloped in a shell, and simulate true ova." This aggregation of 

 several cells (one of them putting on the appearance and fulfilling the 

 functions of a Purkinjean vesicle), and the whole becoming enveloped 

 in a shell, is, however, the ordinary and only method of egg-develop- 

 ment in many lower animals. In theTrematoda and Cestoid worms, 

 and the greater number of the Turbellaria, the yelk and the Purkin- 

 jean vesicle are formed in two separate organs. 



In Piscicola, according to Leydig, the mature egg contains, besides 

 the Purkinjean vesicle and the ordinary velk, a number of nucleated 

 cells (Zeit. f. Wiss. Zool. 1849, part 1. pi. 10. fig. 56). 



In the Mites and Spiders, in Chelifer, Obisium, the Phalangidse, 

 and, so far as I know, all the Arachnida, the egg arises from the 

 metamorphosis of a single cell. 



On the other hand, we find that complex eggs alone are present in 

 vast numbers of insects, namely, in all the Lepidoptera, Diptera, 

 Neuroptera (excluding the Libellulidfe and allied genera), Hyme- 

 noptera, Heniiptera, Homoptera, and Coleoptera. We are as yet 

 ignorant of the mode of egg-development in the Thripsida and the 

 Strepsiptera ; nor does it seem quite clear whether the development of 

 the pseudovum in Aphis can be referred to the complex type. It 

 would, however, appear from the statements of Leydig, Huxley, and 

 Leuckart, that, in the opinion of these three eminent naturalists, the 

 pseudovum is a derivation of a single ovarian cell, and differs there- 

 fore in this respect from the ovum of the impregnated female. 



We know little as yet about the early stages of egg-formation in 

 the Crustacea ; but it would appear that the simple mode prevails 

 generally throughout this class, with the exception of the Daphnidse. 



As regards the Rotatoria, the so-called winter eggs have been 

 observed in Hydatina, Brachionus, and Notommata, as well as in 

 Lacinularia ; and we may probably conclude that in these and other 

 allied genera the development of these eggs is on the same type ; 

 while "summer eggs" are formed from one cell. Among the 

 Myriapoda, the eggs of Lithcbiiis, Cryptoj^s, Geophilus, Arthrono- 

 malus, Polydesmus, and lulus are simple, the vitelline vesicles 

 occurring in some of them being probably homologous with the yelk- 

 nucleus of Spiders. 



Glomeris, however, offers apparently an exception to the rule so 

 general among the INIyriapods, as the large rounded bodies present in 

 the egg-capsule are probably homologous with the vitelligenous cells 

 of insects. 



In excluding the ephippial ova of Lacinularia from the category 

 of true eggs. Prof. Huxley was influenced to a certain extent by the 

 supposition that they are fertile without impregnation, and are there- 

 fore " not ova at all in the proper sense, but peculiar buds." Accord- 

 ing to Stein, however, the reverse is probably the case, and the 



27* 



