1214 MK. F. R. WELLS ON THE MORPHOLOGY OF THE 



Teleostei, more especially of the Olnpeiclfe and Siluridse. No 

 work has been done on the cranial development of the 

 former*. 



Material was obtained from Plymouth, and was fixed on 

 the trawler as it was caught ; the larger stages were caught 

 in Dublin Bay in 1921 ; material was also obtained from 

 Lowestoft. 



I wish to thank Prof. MacBride, Dr. Hogben, and Mr. H. 

 Graham Cannon for valuable suggestions and assistance with 

 both the work and the manuscript. 



2. Method. 



The specimens were fixed in Bouin's fluid, in Chromic-Urea- 

 Bouin, or in Corrosive Sublimate. The first was found to be most 

 successful. A number of series of ti-ansverse sections were cut, at 

 8^ /a; they were then stained in Ehrlich Hsematoxylin, in Borax 

 Carmine and Picronigrosine, in Mallory's triple stain, or in 

 Thionin and Orange G. The last was found to be the most 

 successful. 



The usual wax model method of reconstruction was not used. 

 The reconstructions were made direct as dorsal or lateral 

 views on specially squared paper. The exact method is as 

 follows : — 



An eyepiece micrometer, divided into squares, was used. The 

 virtual size of these squares, with the various powers used, was 

 measured by means of a blood-corpuscle measuring slide divided 

 into hundredths of a blood millimetre. With the microscope 

 used (Leitz, eyepiece 3, objective 3, draw-tube 140) one square 

 was found to measure "15 mm. The reconstructions were made 

 at a magnification of 120. The paper was therefore " squared " 

 with lines 18 mm. apart vertically (or longitudinall}^) and 1 mm. 

 apart (= 120 x 84/^) horizontally (or transversely). The direction 

 of the lines on the micrometer was then set according to the 

 direction from which the view was taken, and the reconstruction 

 mapped out directly on to the squared paper. This method is 

 really a simplification of the method, which was tried at first, of 

 dra,wing each, or alternate, section on squared pajDer and then 

 reconstructing dorsal or lateral views bj? measuring these 

 drawings. The new method merely eliminates the intermediate 

 process. It was found to be very considerably quicker, and 

 certainly as accurate as the wax model method. The same 

 assumption had to be made as is made in the model method — 

 that is, the assumption that one of the cartilages was straight. 

 In the reconstructions made the ethmoid plate was taken for 



* It is interesting to note that none of the above-mentioned tj'pes have lavvas, as 

 do the Clupeoids, Flat-fish, &c. The term " larva " is here taken to refer to the free- 

 swimming stage preceding metamorphosis as opposed to the newlj'-hatched j^olk- 

 sac bearing embryo. Labour and others refer to this free-living stage as the post- 

 larval stage. 



