398 M. Victor Faussek on the Anatomy and 



were laid in autumn, at once commenced to develop at the 

 temperature of an ordinary room, and within one and a half 

 to two months the Aviiole cycle of development was com- 

 pleted, and the young animals emerged and throve perfectly 

 well throughout the entire winter. The ova of Opilio parie- 

 iinus perished under the same conditions, and were capable of 

 further development only after passing the winter in a normal 

 state, when I placed them upon the ground. Besides these 

 two species I also had a few ova of larger size belonging to 

 a species which I failed to determine. 



2. With regard to reagents, Flemming's mixture gave the 

 best results, in addition to Perenyi's fluid and sometimes (for 

 the earlier stages) hot absolute alcohol. I did not study the 

 formation of the segmentation nuclei. The earliest stages 

 which I examined showed the ovum divided up into a com- 

 ])act mass of cells ; in each of the large segments there lay a 

 large nucleus (Taf. i. figs. 6 and 7 of the Kussian memoir). 

 The ovum consequently undergoes total segmentation and 

 passes through a morula stage. The first blastoderm (ecto- 

 derm) cells split oft' from the superficially situated blasto- 

 meres, as is correctly described by Henking*. The segmen- 

 tation nuclei do not come to the surface of the ovum, but all 

 remain within the blastomeres. In the Araneida?, as may be 

 gathered from the investigations of Morin f, total segmen- 

 tation also takes place and the ova pass through a blastula 

 stage, having a large segmentation cavity. In Phalangium 

 a solid morula is formed, and the ectoderm cells are produced 

 by being split oft", as it were, by delamination. 



3. The entire ovum gradually becomes clothed with a 

 layer of flat ectoderm cells, and thus ])as3es into the bilaminar 

 stage. After the formation of the ectoderm the inner egg- 

 membrane (oolemma) becomes considerably thicker, so that 

 two layers can be distinctly distinguished in it, which, how- 

 ever, are closely apposed to one another and never separate. 

 There is an evident secretion of cuticular substance by the 

 ectoderm cells, which gives rise to the formation of a kind of 

 embryonic membrane ; yet this new cuticular membrane does 

 not form an independent envelope, but serves to thicken the 

 oolemma. This subsequent secondary thickening of the 

 memhrana vitclh'nahy the formation of a new cuticular layer 

 secreted irom the ectoderm is comparable to the formation of 



* Ileuking, '' Uutersucbungen iiber die Eutwicklung: der Phalangideu,"' 

 Zt'itscbrift f. wiss. Zoologii', 4o Bd. 



t Morin, " Ueber die Eutwicklung der Spiuueu" (in Kussiau), Zeit- 

 scbrift der Neurussischen Gesellschat't in Odessa, xiii. Bd, (18:>6). 



