212 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Development of Petromyzon fluviatilis.* — Mr. A. E. Shipley differs 

 from Mr, Scott in his description of the formation of the mesoblast, for he 

 finds that the ventral mesoblast is formed by the dowugrowth of the 

 mcsoblastic plates, which ultimately meet and unite in the ventral middle 

 line. Max Schultze was more correct than later observers in stating that 

 the blastopore does not close up, but remains as the anus ; there is no 

 neurenteric canal. Anteriorly the hypoblast remains connected with the 

 epiblast, and here the gill-clefts arise, the mesoblast growing down between 

 them to form the gill-bars. The peculiarly constructed muscle-plates 

 each arise from a single cell of the mesoblastic somites, the nucleus of 

 which divides until each cell contains several nuclei ; striated fibrils then 

 appear to increase till the whole muscle-plate consists of little else ; these 

 " plates " arise from the segmental half of the mesoblast, while the muscles 

 of the gills, lips, and probably of the eye, arise from the ventral unseg- 

 mented part and have a different structure. The blood-corpuscles arise 

 from the ventral free edges of the mesoblast ; the heart appears in the 

 ventral mesentery, formed by the union of the lateral mesoblastic plates, 

 and is at first continuous with a large sinus which lies just behind it. As 

 this sinus acquires walls, it forms part of the subintestinal vein. 



The ciliated funnels of the pronephros are left as apertures, owing to 

 the closing up at intervals of the groove which forms the segmental duct. 

 The canal of the central nervous system developes after the neural chord 

 has separated off from the epidermis, and it does not appear to be lined 

 by any invaginated epidermis. The first sign of cerebral differentiation 

 is the formation on the sixteenth day of the optic vessels and pineal gland ; 

 the fore, mid, and hind brains appear a little later. The ganglia on the 

 5th, 7th, 9th, and 10th nerves are derived from ejiiblastic thickenings, and 

 the ganglion of the fifth divides into two parts which have a common root. 

 The origin of the ganglia on the cranial nerves has no relation to the sense- 

 organs of the skin, which are not apparent in the oldest larvae seen by the 

 author. 



The early development of the skeleton is described as far as the period 

 at which began the researches of Prof. Parker. 



Some Darwinistic Heresies."]" — Prof. C. Vogt, while accepting all the 

 fundamental points on which Darwinism is based, combats certain views 

 which he regards as exaggerated or ill-founded. The idea with which we 

 start, consciously or unconsciously, that nature sets before herself a purpose 

 just as we do, is not just ; he urges, for example, that, similar as all Equidse 

 are, they have a diphyletic origin. To deny this is to deny the facts of 

 geological geography, and any jjhylogenetic tree which does not take it into 

 account is by that fact alone erroneous or null. We must, then, conclude 

 that there is a divergence of characters, and this is true of free-living as well 

 as of parasitic organisms. Metamorphoses take place : (i.) By the reduction 

 and final loss of primordial characters, fii.) By the excessive and unilateral 

 development of other characters which often originally existed only roughly 

 sketched out. (iii.) By changes of function which imply the separation of 

 parts originally united, and the fusion of other parts originally separated. 

 If these statements are true there cannot be harmonious development in any 

 organism, but only relative harmony, one or several organs being pre- 

 ponderant in development. Man himself, where everything is subordinated 

 to the development of the brain, is a proof of this. 



* Quart. Journ. Micr. Sci., xxvii. (1887) pp. 32.5-70 (4 pis.). 



t Arch. Sci. I'liys. ct Nat., xvi. (1886) pp. 3:50-8; trausliikd in Ann. and Mag. Nat. 

 Hibt., xix. (1880) pp. .57-01. 



