AND MORPHOLOGY OF APHIS. ; . 938 
Mollusk. The germ of the Arthropod becomes antero-posteriorly segmented ; the germ 
of the Mollusk never does so. From these two fundamental differences a multitude of 
others necessarily follow. 
The Articulate embryo is no less markedly separated from that of a Vertebrate animal, 
although in the latter, as in the former, it is the neural surface which is first developed ; 
for I know of nothing in the Articulate embryo to be compared with the primitive groove, 
the chorda dorsalis, and the dorsal plates of the Vertebrate*. They, like the amnion and 
the allantois, are, I believe, structures without a representative in the other two sub- 
kingdoms. 
There is perhaps, as Zaddach maintains, a certain analogy between the primitive seg- 
ments of the Articulate animal and the primitive vertebræ (** Urwirbel" of Remak) in the 
Vertebrate, but with the commencing differentiation into tissues the resemblance entirely 
ceases. The appendages of the Vertebrate embryo are more Molluscan than Articulate in 
their primitive mode of development. Notwithstanding all these great and real differ- 
ences, however, there appears to me to be one respect in which a most singular analogy 
obtains between the Vertebrate and the Articulate type :—it is in the construction of the 
head. 
Adopting, in some respects, the views of Prof. Goodsirt, I can recognize at least six 
more or less complete segments in the completely ossified Vertebrate cranium. It is 
clear that the Vertebrate mouth opens like that of the Articulate animal, though on the 
opposite side of the body, between an anterior and a posterior set of cephalic segments. 
In the interior of the cranium a no less natural boundary between the anterior and the 
posterior set of cephalic segments is afforded by the pituitary body and its fossa, when 
the latter exists. 
I find, again, in the cranio-facial bend of the base of the cranium in the Vertebrate 
embryo, something wonderfully similar to the cephalic flexure of the Articulate head, and 
in the cranial trabeculæ (Schädel-balken of Rathke), analogues of the procephalic lobes. 
While fully recognizing the fundamental differences between the Articulate and the 
Vertebrate type, then, I think we should greatly err if we overlooked such singular ana- 
logies as these. Future research will show whether they are or are not the outward 
signs of a deeper internal harmony than has yet been discerned, between the Articulata 
and Vertebrata. 
Since the present memoir was read to the Society, some additional facts of importance | 
have come to my knowledge. In the first place, my friend Mr. Lubbock, having under- 
taken to work out the development of Coccus, was led thereby to search for what I have 
called * ovarian glands" in other insects. His results will be published at length else- 
Where; but he permits me to say that corresponding organs exist in all Lepidoptera, 
Hymenoptera, Geodephagous and Hydrodephagous Coleoptera, Diptera, and most sn 
roptera, while they are absent in Orthoptera, Pulex, Libellulidæ, &c., and are all terminal, 
* I therefore by no means agree with what Zaddach says on this subject, or with regard to the homologue of the 
amnion in Artieulata. 
t As expressed in the Edinburgh New Philosophical Journal, 1857, p. 118 ef seg. 
